How can I find out what graphics card upgrade is compatible with my system?

I have a PC that I got from someone else who built their PC and it is finally starting to show its age. Sometimes when I open applications, the frame rate drops.

I think it is using one of these currently, from 2014. https://www.nvidia.com/en-us/geforce/900-series/

I know that gfx cards have to be compatible with your Power Supply, and your PCI-E slot, but not sure what else I should know??

I would like to get something very compatible with Linux, Firefox, and Wayland, with lots of hardware codecs. Intel ARC?

How do you learn all this stuff?