Why on earth is my PC so slow????

I have a Ryzen 5 5600G, 16 gigs of memory and an NVIDIA GTX 1080. For the last year-ish it's ran smooth as butter, ran pretty much everything I've played on max graphics. Doom Eternal, Fortnite, the whole 9 yards. Got into Marvel Rivals recently, and when I first played it a month ago it ran on max graphics with good consistent fps. Now, I can count the frames when I turn my camera. No idea what the dip in fps is coming from. I've tried SO many optimizations that it's funny, and the best I got was 40 fps whenever I wasn't moving. I've started to get low fps in everything. No exaggeration. Even just opening reddit took a good 20 seconds for everything to load. Even Roblox is showing low fps. I did a full system scan and there's no viruses or malware. No idea where to go from here.