I just want to chime in to confirm all of the above; esp, ≥ WX4100 will work fine, and your security updates will have to be manually downloaded, unpackaged, modified, re-packaged and applied; and even if you have a flashed AMD GPU, you must still reapply patches over the next two reboots.
Also, mysteriously enough, though it draws less power than many cards, it's still going to rev up your primary expansion chassis fan from 600-800 at idle to as much as 1400, unless you take steps to override. If moderate fan noise doesn't bother you, it's of no worry as far as overheating, though the MCH Die Diode gets smoking' hot, and I'm not super pleased with what that means for longevity.
Not even a year ago, before Trump's trade wars took effect (December '20), you could get a brand new Sapphire Pulse RX 580 everyday on Amazon for $169-$179 (I got mine on a lightning deal for $150), and you could find them for as low as $120 used on eBay. If you don't mind paying vastly more today (~3x), it is a better card, and doesn't cause the heat issues. Plus you can pop the extra $130 to have it flashed, and not fool around with musical GPUs with the GT120. Given how stuffed my rig is, that bit was worth every penny (as was the WiFi/BT upgrade back with HS).
Finally, and I advise you to avoid it, Catalina does run on these GPUs, but the OS itself and some 1st party apps are just not great compared to Mojave. I've had some limited success with basic testing and booting of Big Sur, but I'm not holding out much hope it will be worth it.
Though I really would like access to its advancements, I think Mojave may be the end for me; I got my new MP at work, and I am still crossing my fingers that the next Mac Pro with Apple Silicon will offer me what I need at home at a price that isn't completely ludicrous.
Thirteen years, <$5K all-time, and still kicking'; amortize that ****, Tim.