The maximize/minimize/close buttons are missing using regular KDE for desktops (wrong default maybe?)

Describe your issue

The maximize/minimize/close buttons are missing using the regular KDE desktop. Since regular KWin, the non-phone variant, doesn't maximize windows by default and doesn't have other obvious shortcuts for closing windows, this makes navigating windows slightly cumbersome. I'm not entirely sure this is a postmarketOS problem, if it isn't let me know and I'll happily forward it to the KDE bug tracker.

What's the expected behaviour?

The maximize/minimize/close buttons are present using the regular KDE desktop, no matter on what form factor. (I'm currently using it on the Steam Deck, but even on a phone I think with regular KWin you would kind of need these buttons.)

What's the current behaviour?

The maximize/minimize/close buttons are missing. This seems to affect both GTK+ and Qt applications.

How to reproduce your issue?

1. Install postmarketOS on Steam Deck with KDE for desktops (not Plasma mobile)
2. Launch Firefox or KWrite and check the top-right corner of the window

What device are you using?

Steam Deck

On what postmarketOS version did you encounter the issue?

• edge (master branch)

• v24.06

• v23.12 (supported until 2024-07-16)

• I confirm that the issue still is present after running sudo apk upgrade -a

On what environment did you encounter the issue?

Environments

• GNOME Shell on Mobile
• Phosh
• Plasma Mobile
• Sxmo (Wayland/Sway) Please post the output of sxmo_version.sh
• Other: KDE for desktops

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

What's the build date of the image? (in yyyy-mm-dd format)

about one week old

Additional information