Recently installed Linux Mint on an old computer. I put my old RX 590 in it. I only upgrade from the 590 because on every boot on my windows machine I would need to go into adrenaline and underclock the GPU a bit to stop it from crashing when I tried to play games. Adrenaline isn't a thing on Linux so I have no idea how to go about doing this now. Would prefer it just be set there on every boot but I am willing to do it manually each time I start the machine.
I did install the driver from AMDs website but otherwise I'm pretty much at a loss.
Use the default mesa drivers and use corectrl. Depending on the version of mint you're using, you might need to install the appropriate ppas (just google them, you'll find them)
You mean the feature set in the grub config? Their guide on setting up your system to get all the features is quite easy to do and linked on their git lab page