mjhjmtu

Is there any more or less standard/spec that is, vendor neutral, for network configuration language? Say, a VPC with networks and virtual machines would become an XML or JSON file.

Something like,

<deployment>
<vpc name="Test">
<appliances>
 <vm id="1" />
</appliances>
</vpc>
</deployment>

YANG is the answer here. To quote from RFC8345, which defines YANG:

This document defines an abstract (generic, or base) YANG data
model for network/service topologies and inventories. The data
model serves as a base model that is augmented with
technology-specific details in other, more specific topology and
inventory data models.

Protocols like NETCONF can use YANG for representations of network configurations.

Hashicorp's Terraform has a vendor-neutral (but not -agnostic) configuration language. AWS VPCs look like:

resource "aws_vpc" "Test" 
 cidr_block = "10.0.0.0/16"
 instance_tenancy = "dedicated"

 tags = 
 Name = "Test"
 

Ansible can be used to build (part of) a network as code.
It uses YAML syntax and can read JSON.

There's existing ansible roles for major vendor's equipment's, and you can build your own roles.

But existing roles are not always up to date and writing, and maintaining, your own can be time consuming.

For AWS VPCs specifically, you can use CloudFormation to generate a "configuration" file, which can be used to recreate the VPC and all the related components. I believe it's in JSON format.

For networks in general, there is no such thing. Figure out how to do it, and you can retire comfortably.