Thanks zeljko, I have done a quick survery of the VMs I use for testing, with the exception of the U2004 Mate one (my actual work box) they are all pretty much as intended by the distro managers.
In broad summary -
Ones with this problem -
Debian Bullseye in Mate and Gnome
Ubuntu Gnome 18.04, 20.04 and 21.04
Ubuntu XFCe 21.04
Ones that don't have the problem -
Fedora 34 Gnome
Mint 21 Cinnonem
MX 19.3 KDE
SUSE Leap 15.3
Ubuntu 20.04 Mate
All are using their default Window Manager, I tried changing my U2004Mate from Marco to Comwiz and it did not change anything. I changed Bullseye Mate from Marco Adaptive to Marco and again, it did not change.
I believe all the Gnome boxes are using Wayland, I tried changing U2104Gnome to X and it did not change the problem.
I am pretty sure Mate or XFCe boxes are NOT using Wayland. The one KDE on MX is an older release.
So, in summary, it does not seem to relate to either Desktop, Window Manager or Display Manager. Does seem to relate somewhat to the Debian/Ubuntu world. Honestly, I don't think its an issue in the Lazarus Code, otherwise I would log it in Mantis. I think it relates to something missing in the standard install of Qt in some distros. If we can workout what, it can be added as a dependency ! Too easy !
Images below indicate distro, version and desktop in file name. In every case they are running the same binary, compiled with FPC320 and Lazarus Trunk. The test VM set to Adwainta Dark or similar. I have some 11 images but allowed (sensibly) only four, sure you understand I have images to support the lists above. Hmm, wonder if I can identify whats missing with strace ?
Davo