For a little more functionality (but still less complexity than GIMP or Krita), Pinta has a tabbed interface based on Paint.NET. It supports layers, but does not yet support HiDPI:
GIMP's current version (based on GTK+ 2) only has basic support for HiDPI, but their development version (based on GTK+ 3) has full support. I've found it to be quite stable:
https://www.gimp.org/downloads/devel/
https://www.gimp.org/news/2021/05/08/gimp-2-99-6-released/
Krita supports HiDPI, and has a different feature set compared to GIMP:
On a serious note, I don’t have any problems with GIMP, 2.10 is supposed to have hiDPI support. Have you tried Krita and MyPaint?
I usually use Google Drive for this kind of stuff (specifically the Drawing app.)
(Its like MS Paint on Linux but with layers.)
At least for me, Krita has ended up as my paint.net replacement, but it is a step up in complexity from paint.net (and hence two steps up from paint)