For teaching (and for my eyes on a 4K screen), I need sometimes the Eclipse IDE with larger icons and UI fonts (while the editor fonts can be easily adjusted within the Eclipse preferences, the icons cannot and while the UI fonts should be adjustable via Gnome settings, this did not work on my KDE/Plasma system).

What works for me (with X11 -- Wayland is a different thing) is described in https://linux-blog.anracom.com/2024/08/28/eclipse-too-small-icons-on-high-dpi-screens-workaround-for-kde-plasma-by-scaling-on-x11-and-wayland/

• In the KDE display settings (at the very bottom of the configuration dialogue): set Global scale to 125% or 150%.
• (Re-)Start eclipse via

   GDK_DPI_SCALE=0.5 GDK_SCALE=2 ./eclipse &

I also have in my home directory a .gtkrc-2.0 file and need to find out whether deleting it would change anything (i.e. global KDE/Plasma font size setting might then be used, but as long as .gtkrc-2.0 exists, this might override the KDE/Plasma font size setting) -- same applies for the gnome-tweaks command.