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:
Seconding (or third-fourthing?) kolourpaint. Not just the scaling, but I love that it supports true png transparency as just like if it were another color.
http://kolourpaint.org
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:
https://www.pinta-project.com
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:
https://krita.org