I am having the same issue. I also have chartermi.net email and my husbands is charter.net email.
I contacted Charter and they gave me the server name and password as well as the port numbers.
finally found where to set up the emails. control panel-->User Accounts-->mail
I was able to set up 2 other emails connected to my website hosting server but the charter accounts were rejected by "the sender".
Unfortunately, the 2 accounts that were successfully set up do not appear in Outlook. I've closed outlook an reopened and they don't display.
All of these accounts were working in "old Outlook" on my desktop pc. I'm trying to set up a brand new laptop with Windows 11 and MS 365.
I think this is problem with "new Outlook" that Microsoft needs to investigate.