Plasma 6 Wayland with everything from git master. STEPS TO REPRODUCE 1. Be on Wayland 2. Launch System Settings 3. Maximize its window 4. Quit the app 5. Re-launch the app OBSERVED RESULT System Settings launches windowed, at the size it had in step 2. EXPECTED RESULT System Settings launched maximized. ADDITIONAL INFORMATION In step 3, if you resize the window instead of maximizing it, everything works as expected.
Can confirm Fedora 40, Plasma 6.0.4, wayland