Update from Figma support team
Only users with explicit access to a library can actually invite others explicitly
So we can ask friends who already added the library to invite us…
I tried invite myself btw( input my email in the share window) and sometime works sometime failed 
When I failed(I guess it’s because the library is not free open-source) there is a new guest account appear in my account dropdown menu and I’m trying to remove it 
…（update: leave the team option is in the setting menu）