After upgrading Debian KDE from 12 to 13, minimized windows vanish

For the first time since I started using Linux on MEPIS 11 (with KDE 3), I was able to complete a successful version upgrade – in this case, bringing my Thinkpad T430 (Core i5 2.6 GHz, 16 GB RAM, Intel graphics, 320 GB platter drive, side by side with Windows 10) up from Debian 12(.11?) to Debian 13.3 by disabling third party repos, changing all occurrences of “bookworm” to “trixie”, and issuing “apt update” and “apt full-upgrade”, then reenabling distros with update to Trixie as well, and updating/upgrading.

The system starts and runs and everything seems correct – except that if I minimize a window, it’s gone. Doesn’t show in the task bar (which contains System Tray, Icons-Only Task Manager, and Application Launcher), though it is still running, as witness by htop revealing its processes (and allowing me to kill the program).

Is this potentially due to not deleting the .config folder before upgrading (which would require me to redo all customizations on the system, not just the Plasma desktop), or is there something else I can check? Launching an app from terminal and minimizing doesn’t give any additional information, though that does at least allow me to kill the minimized task with CTL-C.

This is important to me, because the next system I need to upgrade is my desktop machine, my daily driver with dozens of installed apps and that I use by preference over both the Thinkpad and my Surface Pro 5 (which got “upgraded” by way of a failed upgrade and install from USB last weekend). I minimize windows frequently, because even with a 2k, 27” monitor, I need to get windows out of each others’ way on occasion.

Where should I go from here?

Okay, I hadn’t tried this because my Thinkpad T430 takes forever to boot – but either restarting to select X11 instead of default Wayland, or just plain restarting fixed this (even after returning to Wayland on a second restart). It must have been a temporary glitch caused by configuring the desktop to match my preferences (Plasma 6 changed a couple things from Plasma 5).