@baxtard @Olat @petsam
Another way to configure the window decorator position in KDE Plasma is to edit ~/.config/kwinrc and find a section called [org.kde.kdecoration2] and modify the two lines to your liking. The letters represent the buttons, so if you move them from left to right, reverse their order as well to maintain familiarity.
[org.kde.kdecoration2] ButtonsOnLeft=XAI ButtonsOnRight=
[org.kde.kdecoration2] ButtonsOnLeft= ButtonsOnRight=IAX
I hope this helps.