Applications use windows-like window management buttons

[Aravisian]

Might try this, given that OnlyOffice uses QT:

Setting QT5/6 apps to use GTK theme in Zorin OS

Updated to be accurate to current Zorin OS: In terminal, download the qt5 plugins and qt5ct configuration tool: sudo apt install qt5ct qt5-style-plugins Once installed, you will need to change some things in Root: sudo -i nautilus or thunar Or... nemo navigate to /etc/profile.d Open qt-style-override.sh and remove the line there, blanking the file. Save and close. next, open `qt-qpa-platformtheme.sh and change its contents to: export QT_QPA_PLATFORMTHEME=qt5ct Close out t…

I am not sure if the version in use in this thread is QT5 or QT6, though...
I just edited that guide to include QT6 instructions.