In the reimplementation of the Present Window effect in 5.25+, selecting windows via arrow keys works sometimes but most of the time it is just not working at all. I cannot say why it doesn’t work most of the time, it feels completely irrational to me. It’s super broken. Only one monitor. X.org session. The fix from 455764 only took it from "doesn’t work at all" to "works sometimes, maybe" for me.
KDE Plasma Version: 5.25.3
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.5
Should be even more fixed with the change to fix Bug 455783.
*** This bug has been marked as a duplicate of bug 455783 ***