Most HighDPI issues on X based DEs is from lack of fractional scaling, which means the scaling needs to happen in the applications instead (with separate configs for each UI toolkit), leading to lots of weird issues with inconsistently scaled UI elements on monitors sized such that integer scaling produces an inappropriate scale.

It doesn't affect all monitors, but some DPIs really don't play well with X. The fractional scaling you get on Wayland leads to some element of blur instead, but that's a far lesser evil, the jank is a bigger issue IMO.