I have been using GIMP 2.99.xx development builds for years now. They are stable enough for what I am doing. I prefer working around their quirks rather than going back to the antedeluvian 2.10 series. What is annoying is all the debug logs/popups and general slowness of the UI, which I suspect is caused by debugging code?
Would it be possible for someone knowledgeable to build 2.99.14 (Windows x64 platform in my case) in release mode and publish somewhere? That would be awesome! Thank you!
The whole point of development releases is to get feedback. As for the pop-ups, if you add the Error Console to one of you docks (menu: Windows, Dockable Dialogs), all errors will show there instead of popping up a message box. By right-clicking in the Error Console and going to Highlight you can even reduce what messages will bring the Console to the front.
You could start by going to Edit→Preferences and look under Debugging.
Others have also complained about the speed of the UI updating,
especially on Windows. Maybe someone with Windows Gtk experience will
volunteer some time to look at it. Actualy it takes a noticeable
fraction of a second here on Linux/X too.
If by “popup”, you mean debug dialogs when an error occurs, I sure hope you report them and not just discard the dialog, complaining they are annoying!
We haven’t heard of particular slowness of GIMP 2.99.x on Windows, but if there is a problem in some cases, we wish to know about these. If everyone using development releases of GIMP just “work around quirks” rather than reporting issues and helping us to fix them, you can be sure that you’ll see the same issues in the finale GIMP 3.0 release. Bugs are not going to magically disappear just because it will be called “stable” so as @jboerema reminds, we need people’s feedback, reports and investigations.