@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.
Change:
[org.kde.kdecoration2]
ButtonsOnLeft=XAI
ButtonsOnRight=
to
[org.kde.kdecoration2]
ButtonsOnLeft=
ButtonsOnRight=IAX
I hope this helps.