I'm using a 3840x2160 screen. It seems that my IDE is mostly working, but the code editor seems to be having problems with HiDPI awareness?

Is this a bug, or a setting I didn't tweak?

Please see the attachment for the screenshot, I'm not sure if it is obvious that the editor part of the IDE is of lower resolution than the rest, but it is.

(Click to enlarge)

Try a different editor font (or a few). Does that change it?

 It didn't change after editor font changing.

But I do observe that the font name in the font selector dialog itself is blurry also.

(Click to enlarge)

Solved: Duplicate with Gambas One - Gambas ONE

Launch with "$ env GB_GUI=gb.qt5 gambas3"

 then it's possibly your GTK font settings.

Try the System GTK "Appearance" settings
System/Preferences/Look and Feel/Appearance

perhaps the monitor does not like smoothing?

(Click to enlarge)

Sometimes I wonder why we persist with gtk. JMPO  

 I have experienced similar issues on a 4K display with 200 % scaling. On one linux distro gambas looks crisp only if I start it with qt5 and another one looks crisp only if I start it with qt6. I like how this can be selected by right clicking the gambas taskbar icon, the functionality is baked in the dot desktop file of gambas.