Brush lag on 4K monitor in Kubuntu when Canvas Graphics Acceleration enabled.

My previous OS was Ubuntu studio 18.04 where drawing worked fine, but some features were lacking or caused crashes like Scripter or Detach canvas. This and also the fact that there is a functional UI for tablet settings in Kubuntu made me change versions. But now the brush lag is unbearable even if I use mouse when CGA is on.

I got gf 1080 and have no lag issues in Photoshop nor in Ubuntu 18.04 the lag wasn’t anything close to what I experience in Kubuntu.
Also the only Krita versions that work at all, are the nightly builds as 4.3.0 version gives me error:

ASSERT (krita): “screen < QGuiApplication::screens().size() && screen >= 0” in file /root/parts/krita/src/libs/widgets/KoToolBox.cpp, line 51

Are there any possible solutions for this so I can zoom and paint?

If you have more than one screen, use the nightly stable build ( since that has that bug fixed.

As for performance problems with 4K screens, see and test the packages linked there.

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Thanks, hopefully Krita’s performance on 4K can be improved.

I wonder to what degree, in my case, is it related to this release of Kubuntu. Is is likely that this could be largely resolved by changing some settings, drivers (currently I’m on nvidia 440), or possibly by switching to Kde-neon?