I'm currently using Manjaro with Plasma 5.19, KFW 5.71, Qt 5.15 and for months now I've had an issue with tiny icons and fonts in the context menu of the plasma desktop on a 4K display so I was hoping an update to 5.19 would fix it. All apps and the panel seem fine and the size of the desktop icons are okay but not the RMB context menu. I think it started when I tried to switch to optimus nvdia a few months ago and then back to modesetting. I've tried various google inspired env vars, X11 and sddm conf settings but nothing has worked so far. My scaling factor is 2.5 and that works well everywhere except the desktop context menus so is there somewhere in the overall desktop startup sequence where I can add a scale or dpi setting to affect the RMB context menus?

It's a known issue on X11, see https://bugs.kde.org/show_bug.cgi?id=356446