With LO-fresh I tested as follows:
Test 1: The focus was on the undocked window – Ctrl+Shift+F10 worked.
You are not using a same custom shortcut, I hope.
Test 2:
Closed undocked window with Alt+F4
Ctrl+F5
Ctrl+Shift+F10 also makes sidebar in docked mode visible.
(Finally in View (Alt+V) / Sidebar checkbox also may help if it is ‘lost’.)
Done on an updated Plasma wayland. Did I misunderstand the problem?