Bring features from the "Old" theme to the "New" theme.
For all OS.
Back in GIMP 2.10.32, all themes except "System" had this great feature to it where, represented by three black/white dots, it shows where you can aim your mouse at to resize a window.
Said feature is not available in 2.99.14 anymore.
Also, it seems that the size is inconsistent between old and new GIMP, which is not favourable, this is visible with the icons' size that seems to auto-scale the context and tool windows. The colour on current Gray theme is also very inconsistent, it seems that now it's impossible to get a proper "Neutral Gray" like on GIMP 2.10.32, the current gray is a mix if lighter and darker grays.