Created attachment 166246 [details] Screen-Capture This might be more of a question than a bug report as I have no idea what's going on. I tried to re-install the non-flatpak version of LO on Linux Mint using the Software Manager. And, starting LO for the first time, the UI elements were extremely ugly. See attached screen-capture. I tried re-installing LO a couple of times. I tried to uninstall/remove all LO-Packages I could find. Nothing could change the look of LO. Was this just the way LO 6.4.6 looked? I was sure, it was more modern-looking!
Could you give a try at https://wiki.documentfoundation.org/QA/FirstSteps?
You are missing a VCL backend. Probably you want libreoffice-gtk3 package. If in doubt, please ask for help in Linux Mint forum or similar channel.