How do I fix missing email account and sync issues on a new Mac mini?

On a new Mac mini m4 was trying to get emails to sync with my iPhone and iPad. I am using optimum email. It was set to pop on Mac mini and imap on the other devices. Could not change the settings so I deleted the account. Then tried to add a new mail account. It says that the account already exists, but does not show any mail or list the account. I need some help

[Re-Titled by Moderator]

Original Title: Email is gone