You can add anyone to a Team in Microsoft Teams as an owner, member, or guests. Guests are external to the Drexel organization (not students, not employees, not faculty, not paid researchers). No one can have access to a channel in a Team in Microsoft Teams if they are not a member, guest, or owner for that Team. However, you can use Private Channels if you want select members and guests of that Team to see that channel and its contents.
Creating Standard vs Private Channels.
Private channels have select members or guests only with access to that channel, rather than everyone in the team, like a Standard Channel.
Permission Level Differences for Team Roles Explained
Add guests to a team in Teams
Set guest permissions for channels in Teams
Add Regular Team Members