I tested some more, and the issue seems to be more complex than I indicated in comment #14.
Some XKB shortcuts for switching input source work in both Wayland and Xorg. Examples are:
<Caps Lock> <Left shift> <Left alt>
i.e. if you define a single modifier key for the purpose it works.
<Alt>+<Shift> is a problem on wayland at least, and when I tested in a VM it failed to work on Xorg too.
Also <Ctrl>+<Shift> is problematic (on Wayland).
I tested some more, and the issue seems to be more complex than I indicated in comment #14.
Some XKB shortcuts for switching input source work in both Wayland and Xorg. Examples are:
<Caps Lock>
<Left shift>
<Left alt>
i.e. if you define a single modifier key for the purpose it works.
<Alt>+<Shift> is a problem on wayland at least, and when I tested in a VM it failed to work on Xorg too.
Also <Ctrl>+<Shift> is problematic (on Wayland).