CPU temps and fan speeds look ok. You could run the free version of Malwarebytes.  It only runs when you launch it and won't interfere with your full-time antiviral app. Have you gone to the forums for your games or for you new video card to see if anyone there is having slow-downs?  Is there a newer video card driver? Maybe I missed it, but are you playing these games alone on your PC, or are you playing online?
So I currently have a problem where when I play fortnite, the first 10 or so minutes performance and everything is perfect. However, past that i start getting fps drops. I though it was my GPU so i then replaced it for a Gefore RTX 2060 and that helped a lot temporarily. But then the fps drops and lag started to persist dramatically. It happens gradually time as I continue in a gaming session on my pc. I then started to notice in task manager fortnite is taking up high power usage and high power trend aswell as around 70% CPU usage and very high memory as well. I tried overclocking GPU but to no avail the problem persists. Can someone please help me?
XPS 8700, slowly loses performance as I game