The NVIDIA thing has been answered elsewhere in the thread, so I'll answer the other one: ... It depends, but usually there's a minor performance hit. Other times it works just as well, and there are some edge cases where it actually works better.

There's also the issue of compatibility: in general, if anti-cheat software is involved, expect to have problems. This website is a database for Steam games with reports from users about what works, what doesn't work, and what can be done to fix or at least mitigate what doesn't work. You can sync your Steam library to it to see how well the games you have are supported at a glance.

NVIDIA works fine for regular use (including gaming and training ML).

Mint makes changing to the propriety drivers easy, as you just search for and open the drivers screen, and then select the latest propriety driver. Mint will take care of the rest.

Now, I haven't used AMD in a long time, so I'm not sure what it has that NVIDIA doesn't since I haven't experienced any NVIDIA problems, other than open source drivers.