a) Internet provider is an incredibly generic term. It can mean your wireless phone provider, residential internet provider, hosting company, etc. So I’m not clear what is being asked.
b) If Digital Ocean is your hosting provider, then this is the most likely cause of problems related to ports. Note that assuming in the command line installation of MiaB the server provided confirmation of a successful installation, it is highly unlikely to be a problem related to Ubuntu 18.04.
c) MiaB is intended to provide complete auto-configuration of the server, including the server’s firewall configuration. Based on the message reported in the GUI system checks, it is unlikely that MiaB is the cause of this problem.
It is generally not recommended to make custom changes to the ports unless you are an expert and intend to maintain your own unsupported customizations of MiaB.