I am also working with Arch, but I am pretty sure that xbindkeys uses X. So only X sessions (I think XWayland too) can send keys to xbindkeys.
With the KDE 6 update, the plasma-session-x11 and plasma-session-wayland were removed, now there is plasma-workspace.
So the default session is Wayland, but Brave or Thunderbird may still use X11 (XWayland). The result of that is that the KDE Apps (that run under native Wayland) aren’t supported by xbindkeys (as it needs X11 and not Wayland), but all apps that run under X11 (or XWayland) are supported by xbindkeys as they all have the X server.
The solution for this problem might be to just use KDE’s system settings. There you can, under Keyboard > Shortcuts, define a new shortcut that is linked to a shell script which activates that window.
But this narrows down to: How to activate a wayland window by title.
I’ve used wmctl for this but it list only windows of XWayland so I can not activate ie Konsole.
I’ve googled around and did not find a way to do it.