How do I start LibreOffice with a different VCL?

[EyalRozenberg]

How do I start LibreOffice, with a different VCL than the default? e.g. kf5 instead of gtk3?

Notes:

• On a Debian-based Linux distribution
• LO downloaded and installed from the LO website, not the distribution-provided version.
• I’ve installed all .deb files, so all relevant VCLs should be available to me.

[ajlittoz]

Your question is ambiguous. So, edit your question. Don’t add information with a comment.
Which is your desktop manager? KDE Plasma (which uses Qt widgets in the kf5 framework) or GNOME which uses GTK+ widgets.
Have you installed the libreoffice-kf5 package? This is the name in Fedora, may be different in Debian-based distros.

There is usually no reason to launch LO with a different VCL if all libraries are correctly installed. LO detects the desktop configuration and launches the corresponding VCL (if it exists). There is a command line for forcing a specific VCL but it is not recommended unless you know what you’re doing.

[Villeroy]

SAL_USE_VCLPLUGIN=kf5 /opt/libreoffice7.2/program/soffice

If you want to make this persistent edit the same soffice script adding

export SAL_USE_VCLPLUGIN=kf5

I prefer the generic tool set:

SAL_USE_VCLPLUGIN=gen