Dude you're not changing any configs by trying it, it's already installed. You're just selecting an existing option.

Far be it from me to discourage good backups though.

To answer the question no timeshift won't roll it back because there is no change to rollback.

Think of it as grabbing your tv remote and switching the input on your tv from hdmi1 to hdmi2 to swap to the ps5/xbox from the cable box. You're not changing the config you're choosing an alternate input that was already there.

Now if it goes badly (I'll be shocked if it does) then there is a simple way to revert, use your ctrl-alt-f4 (or f3 or f5) keys to swap to a fresh terminal login, login, then type

shutdown -r now

And hit enter

You'll be back after the reboot at the login screen, click on the little mountain icon and choose x11 again (it remembers your last choice) and you're sorted back into x11

Now just to close the loop for when you do need to restore a timeshift backup. Yes it is best practise to boot from a live mint usb & run timeshift from there to restore your last snapshot however in an emergency it will work to initiate the restore from the boot itself (it will initiate a reboot and do it on reboot).

Lastly if it's an AMD gpu I'm betting on hardware, changing that cable and swapping physical connection ports would be top of my list.