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“Observe” oftentimes causes a lot of confusion for this exact reason. It doesn’t actually refer to some conscious entity making an observation.

Rather, think about how we actually make an observation about something. You have to interact with the system in some way. This can be through the exchange of photons, for example. This interaction is what constitutes an observation having taken place.

Obviously, particles can undergo their fundamental interactions without a nearby sentient entity.

For the sake of analogy, consider measuring air pressure in a tire. In the process of doing so, you let out some air — changing the tire pressure in the process.

The Copenhagen interpretation isn't an essential part of quantum mechanics. It isn't required in order to make physical processes happen. It's just a way of describing what seems to happen when an observer makes a measurement. It's not even the only way of describing what it seems like to the observer.

However, according to the Copenhagen interpretation, any random quantum phenomenon only occurs when the system is observed; [...]

If you don't use the Copenhagen interpretation, quantum mechanics still works fine. In your example of the early universe, all the quantum-mechanical processes work in the same way. E.g., a hydrogen atom in an $n=3$ state will radiate light, and at a later time it will be in a superposition of $n=2$ and $n=1$. No randomness, just a superposition.

[...] before observation, the quantum state is symmetric.

I'm not sure what you mean by symmetric here. This seems like a nonstandard description.

"Observation" is not about a human actually viewing and consciously perceiving a system. If one state is capable of affecting another state, then the latter is said to be measuring, or observing, the former. The reason conscious observation also constitutes measurement is simply because interaction with the environment is fundamentally necessary for our eyes to be able to perceive an event.

The Copenhagen interpretation is nothing but an impediment to understanding quantum mechanics. There is no such thing as "wave function collapse" within the system described by QM, nor in any falsifiable physical sense outside of the theory. At best it's an artificial glue for sticking quantum and classical models together; less flatteringly it's a mental crutch for people who don't want to accept that the best model of physical reality we can hope for describes not the evolution of a single deterministic state, but rather the deterministic evolution of a probability model of possible observed states.

Ultimately what's attributed to "wave function collapse" from an act of observation is just conditional probabilities, or if you want to go even more basic, correlations between random variables. I like to explain this via analogies with other applications of conditional probability, and usually end up picking something morbid like cause of death. As a random member of a general population, you have some $X$ percent chance of dying of a particular disease. If you get DNA tests done, you might find out that you instead have a $Y$ percent chance of dying from it, where $Y$ is greater or less than $X$. No physical change took place when you had the test done to change the likelihood of dying from that particular disease. Rather, you're just able to make better predictions based on correlations.

Now, neither QM nor any other physical theory is going to tell us much about what fine-grained observations could have been made in the very early universe, because the correlations to anything we can observe are going to be too small. But that doesn't mean the probability model didn't evolve the same way then as it does now, with all the consequences that entails.

If the Copenhagen interpretation is correct(unknown), and if it requires conscious observers(unknown), our observations of the universe could retroactively collapse the superpositions. https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser .

If only an act of observation by a conscious (whatever it means) creature could cause a wavefunction to collapse, then it would be impossible in the first place for conscious creatures to develop in the course of history because the entire Universe would be in a continuously developing superposition of states without any collapse taking place (collapse is a necessary condition for conscious creatures to develop). Which means that conscious creatures making an observation aren't the cause for the collapse (and nor can conscious creatures now cause the collapse at the beginning of the Universe retroactively because conscious creatures couldn't have developed if the collapse is caused by them). So when inflation took place, no conscious creatures were needed to make a wavefunction collapse, and as you stated in your question, obviously there were no conscious creatures (if the collapse is caused by "a thermodynamically irreversible interaction with a classical environment" then by the same token, neither a classical environment will be able to develop).

This means, for example, that the pattern of lines (resulting from the collapse of a whole lot of wavefunctions corresponding to photons) appearing on the screen in the double slit experiment will develop independently of some conscious creature observing the setup.

This doesn't necessarily mean though that an observer(creature)-independent interpretation is one that postulates a pilot wave (or hidden variables). The "inherently probabilistic" interpretation will do as well. Both can make a wavefunction collapse without an observer. I think which interpretation corresponds to reality will remain unknown (unless someone comes up with an experiment to make a decision which I find hard to imagine) and be a question of "taste". Einstein was an advocate for a theory that underlies the apparent probabilistic behavior of matter ("Gott würfelt nicht", that is, "God doesn't play dice"), as a theory of hidden variables does (somewhat like the molecules surrounding a Brownian particle make the particle move in an apparent random way). But many others (like Bohr in the "famous" Bohr-Einstein debate) take an opposite stand.

For an interpretation of quantum mechanics that requires "conscious observers", you can assign our present-day astronomers that role. Certainly their observations are not done at the time of the early universe itself. That's just fine. No problem if you observe 15 billion years after the fact.

The problem only exists if you insist that observations must be done simultaneous with the observed phenomenon. But simultaneity has no place in physics, such a requirement would be at variance with basic physics (relativity). Quantum mechanics does not use simultaneity, and does not prescribe when observations must be made.

Observation does not mean "by a human". Observation is any action on the system by outside of the system. Photons interacting, the confines of the system being changed, etc.

Your comment above about superposition "automatically collapsing in the early universe" is wrong. A hydrogen atom with superposition of it's energy level will collapse when the value of it's energy level is needed (e.g in a physical collision) which counts as an observation. The main takeaway is that when we say observation we mean interaction with a clearly defined outcome.

The problem with this question is that it assumes there is some metaphysical interpretation that we can be sure is true. While we have excellent equations that work incredibly precisely, we are not sure which qualitative interpretation of these equations is real.

There are now countless interpretations, each with their own sub-interpretations. Alexander R. Pruss splits these interpretations into two main groups - No collapse theories with a deterministically evolving wavefunctions and wavefunction collapse theories.

Out of the collapse theories, we have the Copenhagen Interpretation, where the wavefunction collapse is triggered by a measurement. Definitions of what constitutes a measurement can differ a lot depending on the physicist/philosopher. The Ghirardi-Rimini-Weber theory is another collapse theory where the collapse is triggered at some particular rate over time. The trouble with this theory is that no spontaneous collapse has been observed in any way, and an additional parameter - that of the rate of collapse - has to be introduced and explained in some way.

There are also many no collapse theories such as Bohmian Mechanics, the Many Worlds Interpretation, Many Minds Interpretation and Traveling Forms interpretation. In these, the universe continues to develop deterministically, but each have their own reasons as to why we can only get stochastic results from the deterministic systems upon measurement. Each of these interpretations also have their own problems. Bohmian Mechanics has the problem of nonlocality. The Many Worlds Interpretation is unclear as to how splits occur and is a bit bizarre to try to reconcile with, for example, the conservation of energy. The Many Minds interpretation leads to bizarre absurdities such as Boltzmann Minds and universes where there is just one mind surrounded by zombies. I don't think the Traveling Forms is well enough known to have its own critique, but I expect someone will come up with one at some point.

I found an excellent study of this topic in this book: http://www.michalpaszkiewicz.co.uk/blog/reviewnapocs/index.html

As others have mentioned, your definition of observer seems to have mislead you.

Take the double slit experiment for instance. In this case, the observer which forces the wave function to collapse is the screen, not the person looking at the screen. The results would be the same without a person looking at the screen.

It's an interesting question - with no answer

Your asking about quantum effects in the pre-inflation universe, which could have been as small as $10^-26m$. We are talking about a very massive and extremely small system, which would be described by a theory that unifies general relativity and quantum mechanics. As of now, we just don't have this theory, so anything might have happened. At least quantum theory probably does not apply.