Hello!
The GUI is mainly managed by Mono and this problem is not reproducible on our and our customers' Linux systems. Specifically, one of our testing systems is Debian 13 with KDE Plasma 5, and we don't see any problem at all. However, our DEs run on X.Org server, not on Wayland. Eddie and Mono may have various problems with Wayland on Debian 12, just like a lot of other applications have. You can consider to switch to X.Org.
Can you also tell us which compositor is used in your Plasma environment (in Plasma, this is typically KWin)?
Next Eddie GUI will not need Mono anymore and Wayland compatibility will be improved, but probably not on systems with archaic packages like Debian 12 (see below).
But you can consider to upgrade to Debian 13. Debian 12 Wayland support was not ready for everyday use, while things improved on Debian 13. Also, Debian 12 regular security support ended on June 2026 and its kernel is very old, therefore upgrading to Debian 13 is in any case a good idea if possible. Also consider that Debian 13 is now the main development platform for Eddie Linux edition.
Kind regards