I guess I need some help understanding VM's.  I have a few running, and if I edit the configuration, each one has a Primary vDisk Location which points to a single file.

 

Is this file the entire VM setup, including any changes that have been made while accessing that VM and its features?

 

For example, if I back up the .qcow2 file in the /mnt/user/domains/home_assistant/ path, what am I actually backing up, and what am I not?

A vdisk is a file that is emulating a single physical drive and it stores whatever whatever would be the case on a physical drive on a physical machine.

17 hours ago, arretx said:

if I back up the .qcow2 file in the /mnt/user/domains/home_assistant/ path, what am I actually backing up, and what am I not?

You are backing up the "hard drive" of the virtual computer but not the type of motherboard and other emulated hardware, or other details about the virtual system. Think of it as a custom built PC, if you restore the hard drive to a totally different system with different CPU, more or less RAM, a different video card, a different network card, etc, it may boot and run, it may not, but it will definitely know it's running on different "hardware".

 

If you also make a copy of the XML that is used to define those items, the XML that you reference here,

17 hours ago, arretx said:

I edit the configuration

you can use that XML (seen in advanced edit mode) to recreate the exact virtual system. You may also need to back up any other files besides the main vdisk file if any are referenced in the XML.