Open Network Ports on 5G Network

I've spent the past couple of days calling AT&T customer service about open network ports while using their wireless 5G network. I used a couple of apps with network tools to do a port scan on my assigned external IP and found ports 21, 80, 443, 554, and 1723 are open. AT&T's Advanced Tech Support is unable to provide me with a valid reason for these ports being open. All they can tell me is the ports can't be disabled and are necessary for the service to work.  What services are offered that require these ports to be open? Ports 20, 554, and 1723 have known vulnerabilities. Can anyone provide any additional insight about why these ports have to be open to use the 5G network?