lebout2canap ⏚ on Nostr: ALT+TAB is another way to work around the problem that also works for me, and indeed ...

ALT+TAB is another way to work around the problem that also works for me, and indeed it allows me to return to the same desktop without the mouse being captured by Lix. So technically this answers my question, but I would have hoped for a more satisfactory solution: in the case of DOXBox (and its successors) (where mouse capture makes sense) for example, a Ctrl+F10 or a middle click is enough to release the mouse.