mail won't work with Sequoia
I have 2 mail accounts. One works (iCloud) and the other one doesn't. I just setup a new iPad. It has the same problem.
iMac 24″, macOS 15.1
Are you creating a new mail account for the first time to use in Apple Mail? IF for the first time, you may need to go to the provider for technical assistance to get settings, especially for POP, IMAP is usually preferred and simpler. Some email accounts like AOL require one time app pass words to use with Mail, etc, which is not needed with web-mail. IF you had it working before under Sonoma, it will be working under Sequoia.