Roundcube Installer Warning: "Mimetype to file extension mapping: NOT OK"

I got Roundcube up and running on my CyberPanel managed server, but I noticed this warning in Roundcube’s installer in the third and final “test config” step:

Mimetype to file extension mapping: NOT OK

Roundcube itself runs fine, but I would like to know what this means and how to fix it. How do I fix this in CyberPanel with OpenLiteSpeed?

maybe this will help?