Th0mC yes those folders can be excluded. composer-home is part of the Bazaar extension and can also be excluded, it's just cached data.
In a base Flarum, all folders in storage can actually be excluded without any issue (cache, formatter, less, locale, sessions, tmp, views). Only storage/logs holds data you might want to not lose. Other extensions might create their own folders with important data.
Likewise you can safely ignore the vendor (and vendor2 folder if Bazaar created one), as those can easily be re-downloaded from the composer.json+composer.lock files by running composer install.
Some automatically generated files (<admin/forum>(-[lang])-[hash].<js/css>(.map)) in public/assets can also be excluded from backups, but it might be a bit tricky to remove just those and make sure you keep all the extension data in there.
