Dear nNici
Thank you for posting in the Microsoft Community.
I understand your situation and your needs. This is due to the fact that Microsoft currently requires the new authentication style to connect to all mailboxes on Microsoft domains such as Outlook, Hotmail, Live, msn.
First, your macOS system needs to be updated to macOS 12 or later. Next, you'll need to remove the Microsoft domain account from your email. Then click Add Account. Select Microsoft Exchange. Enter your account name.
The system will automatically switch to the Microsoft interface to request to connect. Upon successful login, it will automatically switch to new-style authentication and can be used normally.
You can refer to this link to learn more about the new authentication style.
I hope my answer will be helpful to you.
Feel free to let me know if you have any other updates, thanks.
Sincere greetings
Simon.W - MSFT | Microsoft Community Support Specialist