Fresh install of LO 188.8.131.52 on a fresh Win 10.
Open a new document (writer, calc, draw, ...).
In the sidebar or format toolbar, there are 3 dropdown menus : "style", "font" and "size".
1) Clicking in any of these dropdowns does nothing. The selection is not changed, nor the dropdown's text.
2) Clicking in the scrollbars (when present) closes the dropdown.
3) Clicking in a dropdown and using the keyboard arrows to change the content does work.
The other types of controls seem to work (didn't test every toolbar).
Fixed towards RC2.
*** This bug has been marked as a duplicate of bug 96119 ***