Found out that this error is upstream: https://bugs.kde.org/show_bug.cgi?id=493147 It defaults to max refresh rate 144Hz and Adaptive Sync setting Automatic when using HDMI. Setting Refresh Rate to 120Hz solved the issue.
- Bug#1098457: kwin-wayland: Black screen when Adaptive Sync is ac... Are Mehus
- Bug#1098457: Upstream error Are Mehus
