MasAntok For better understanding, please see attached images. For example, php-intl has been installed but s9e/text-formatter suggests installing ext-intl
luceos MasAntok the suggestions are just that, they are optional. They are meant to give a hint on what you could also install to get additional functionality working in the dependency. Now although you installed the php extension, it seems composer is misbehaving as it doesn't detect that the requirement is already met.
MasAntok luceos so this suggestions can be left as is, right? Everything works perfectly at my local install, not found any error so far. Will back here if need some directions how to use / customize Flarum.