Yes - this is all a combination of the packaging of Ubuntus LO version, the default packages being installed by Ubuntu and your desktop manager. Most probably you haven’t installed GTK3 support for LO (libreoffice-gtk3).Please check
user@system:> dpkg --list libreoffice-gtk3
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
un libreoffice-gtk3 <none> <none> (no description available)
If it is “un”(installed), install it using:
user@system:> sudo apt install libreoffice-gtk3
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