Aren't most immutable Linux distros AB, almost by definition? If it's immutable, you can't update the system because it's immutable. If you make it mutable for updates, it's no longer immutable.

The process should be:

1. Boot from A
2. Install new version to B
3. Reboot into B
4. If unstable, go to 1
5. If stable, repeat from 1, but with A and B swapped

That's how immutable systems work. The main alternative is a PXE system, and in that case you fix the image in one place and power cycle all your machines.

If you're mounting your immutable system as mutable for updates, congratulations, you have the worst of immutable and mutable systems and you deserve everything bad that happens because of it.

idk if it would be manual, isn't the point of ab root to rollback if it doesn't properly boot afterwards?

Honestly if you're managing kernel and userspace remotely it's your own fault if you don't netboot. Or maybe Microsoft's don't know what the netboot situation looks like in windows land.