The keyboard shortcut Ctrl+F12 does not work for ungrouping data. Ungrouping data is possible only through the menus. However, F12 works fine for grouping data.
For me on KDE Plasma, Ctrl+F12 is a desktop-wide keyboard shortcut for "Show desktop". Thus it does not work in LibreOffice. Is this your problem as well?
(In reply to Buovjaga from comment #1) > For me on KDE Plasma, Ctrl+F12 is a desktop-wide keyboard shortcut for "Show > desktop". Thus it does not work in LibreOffice. Is this your problem as well? I am using XFCE, whit Ctrl+Alt+D mapped for showing the desktop. However, your hint helped me discover that Ctrl+F12 was mapped for showing Workspace 12. Now the problem is solved. Thank you very much!