Mac Mail App "Unable to Verify Account Name or Password" and "This Account Already Exists"

Following a password change on our ISP (Bell) Email Account, we were able to successfully implement the change on all our devices except for the Apple Mail App on our MacBook Air. (iPad, iPhones, Webmail, Windows devices all fine.) Upon making the change on our MacBook Air, the Mail App said "Unable to Verify Account Name or Password". Tried removing the account and adding it back in. This time it would not allow us to add in our account, saying "This Account Already Exists" (even though it was not showing). With excellent help from Apple Tech Support (first level and then senior advisors), we tried various things, signing out of Apple ID, and back in, trying Safe Mode, downloading MacOS again, confirming no malware, etc. To allow us back in via the MacOS Mail App, we had to create a new user login on the MacBook Air, and add the email account (which worked fine), and then log in to our existing Apple ID via that new user. Everything is working again. (I am reluctant to try to change the email password again to check out if it would work properly after another change.)

Many Apple users found the same issue with "Unable to Verify Account Name or Password" and "This Account Already Exists" on their Mac Mail App, based on various forum reviews. In our case, Apple Support attributed it to some glitch in the particular MacBook user account. But, given the number of people who have run into this, it sure seems that there is a bug in the Apple system that should be fixed to stop this "glitch" from happening for so many users. To have to spend almost two full days troubleshooting, just because we wanted to change the password on our email account (as a good practice periodically) is not right.

I am writing this to:

-Let other community members know what we went through to resolve this, in case they are in a similar situation and are interested in trying the resolution that worked for us.

-Ask others in similar situations what their experiences/resolutions were and what resolution they found.

-Let Apple see that this issue appears to be a continuing "bug" that affects a large number of users and it should be investigated and repaired.

-Encourage Apple to make it easier to change the password for Email on the Apple Mail App, and further to work to update the interface for Settings/Preferences on the MacOS Mail App to look and behave more like on the iOS/iPadOS systems.

-Acknowledge the excellent and timely support that Apple Technical Support staff provided during the resolution of this issue for us over the weekend. Really outstanding and greatly appreciated.