FVM only merges and minifies code, it doesn’t remove anything.
You need to hire a developer or use another plugin to remove unused css/js code (manual process) before you use FVM to minify and merge the remaining files.
For example, https://www.ads-software.com/plugins/wp-asset-clean-up/
Also, pagespeed is likely telling the percentage of code that is not in use, not that the whole file is not in use. Even if one line is in use, you still need the whole thing as you cannot edit plugins and remove it.
It may not be used on that page, but it will certainly be needed somewhere else… hence you need a developer for that part.
