Today I performed a hardware upgrade (ASRock B450M Pro4, Ryzen 5 3600, 2x16GB DDR4-3200. Kept my GTX770 and SSD for now) without reinstalling Ubuntu and now even scrolling websites is lagging severely.
I ran an apt update/upgrade and reinstalled the newest Nvidia driver. I also found the suggestion to run
sudo update-initramfs -u -kall somewhere but that didn't change anything. On Windows (same SSD) everything works fine so far, so it shouldn't be a problem with the hardware I assume.
Any ideas what else I can try besides reinstalling Ubuntu?