Hi all and thank you for this website,
I'm using linux mint since 2017 and had no major problems with it.
Installing the newest Mint 20.1 Cinnamon in January 2021, it came to me with a *laggy interface* especially using Javascript-powered web form inputs (slack chat input for example) and Rubymine (my development IDE based on Intellij Idea).
Here is the trick :
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In the Driver Manager, I was using the recommended proprietary nvidia-driver-460 (460.32.03-0ubuntu0.20.04.1)
Changing to the open-source xserver-xorg-video-nouveau (1:1.0.16-1) removed all the lags !
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PS : A lot of reditters had a similar problem, but instead of replying to many threads, I think your website is a better place to hold this info.