SUMMARY
With Plasma 6.1 from git master, I noticed that the bindings I have set up for the additional buttons on my mouse no longer work, they just end up doing the default action bound to them. In my case the buttons are recognized by libinput as `BTN_EXTRA (276)` and `BTN_SIDE (275)`.

If I revert the part of commit bf1ce854748bfd2433c336a9ee972883cb8617ab (Make it possible to build KWin without libxcb) that applies to the buttonrebinds plugin then the bindings work again, and reverting KWin to the commit before that also works.

In the system logs, these messages appeared when I pressed the mouse buttons (two of these messages appear for every button press):

> kwin_wayland[42047]: kwin_buttonrebinds: Could not convert QKeySequence("Meta+G") syms:  QList(285212743) to keycode
> kwin_wayland[42047]: kwin_buttonrebinds: Could not convert QKeySequence("Meta+G") syms:  QList(285212743) to keycode
> kwin_wayland[42047]: kwin_buttonrebinds: Could not convert QKeySequence("Alt+F1") syms:  QList(150994992) to keycode
> kwin_wayland[42047]: kwin_buttonrebinds: Could not convert QKeySequence("Alt+F1") syms:  QList(150994992) to keycode



STEPS TO REPRODUCE
1. Have a mouse with extra buttons that can be configured via the "Re-bind Additional Mouse Buttons..." page in the Mouse KCM (mine is just a random "gaming" mouse I picked up in a nearby store, with two side buttons)
2. Set up a binding for one of those mouse buttons (I used Meta+G and Alt+F1 for the desktop grid and app launcher)
3. Press the mouse button with the binding

OBSERVED RESULT
The button acts as if no binding was set and just performs the default action (for me the buttons act like forward and back buttons of some sort out of the box).

EXPECTED RESULT
The keyboard shortcut bound to the button should be triggered.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.0.80
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.8-arch1-1 (64-bit)
Graphics Platform: Wayland