Office server controlled by XWiki write files outside of XWiki (permanent, temporary) folders

Following info provided in XWIKI-23797, I tried to create a folder .cache/dbconf and restrict its access locally before starting XWiki jetty/hsqldb with LO autostart. Never got any warning or error and I've been able to properly use it. I tried with LO 7.5 and 25.8.4.2.
I then googled a bit on the warning error "Fontconfig error: No writable cache directories" and found that there was a tool fc-cache listing the cache directories for fonts. I found that one of the directory was .cache/fontconfig so I also tried locally to restrict its access and perform same step than before.
Yet again I haven't been able to reproduce any failure.

So I'm not sure there's something to do: we could want to be able to set an environment variable to the proper directory for this (no confirmation but FONTCONFIG_CACHE might be used for that), but sounds like it could be something to do at system level and not directly related to XS.