Emacs 29.4, Windows 11 Pro — Ctrl is lost

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The undo command in Emacs is C-_ — meaning to press Control and the underscore at the same time. In Neo terms this means: Ctrl+Caps+v (where v would be labeled "w" on a qwerty/qwertz keyboard).

But this only types an underscore.
Emacs also has a testing tool via C-h k (first pressing Ctrl+h then release all keys and now press k). This activates the listener for key combinations. I try my inputs there and see that only the underscore arrives. It has no problems detecting Alt+_.

Any ideas why this might happen? At what point is the Ctrl key consumed?

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I should say that many key combinations do work which involve pressing Ctrl.
It seems to arise when it is combined with the M3 key.
I just tested it with Ctrl+Caps+v and I tried Ctrl++v and both didn’t work.