one way it might help try checking is via your audit logs on how many users are created
I agree the documentation was little confusing
This was an issue recently that many have reported after the change of quota limit introduction itself..but the limit is not shown as you mentioned
as mentioned here once quota reaches you need to upgrade but in case you are not willing to buy you can create…if you want to buy a plan or upgrade to enterprise trail can try that too..but again after the trail period it returns to free
or other way is contact support team where you might need to give a license code which in the case of community would not be available..
cheers