If I minimize gajim by either Escape or click on the close-window in the upper right corner, gajim minimizes as it should, but when I click on the icon in the status tray only creates extremely small window, height is a few pixels, width about 30-40 pixels. (So not even a header.) When I click on the icon again, the small 'window' disappears as it should. I've tried to start without .config/gajim, but there was no change in behaviour. I use Xfce4 4.20.
I believe this upstream bug report is related: https://dev.gajim.org/gajim/gajim/-/issues/12165 (I have the same issue, also XFCE).
For me it is now fixed (in 2.1.0-1, the current Gajim version in Trixie).