Unable to add O365 email account.

Hi uchi123,

thanks for the update.

Here are some additional steps you could try:

1. Reset Microsoft 365 Apps for enterprise activation state: This can help refresh the activation state of your Office apps.
Reset activation state for Microsoft 365 Apps for enterprise - Microsoft 365 Apps | Microsoft Learn

2. Uninstall and Reinstall Office: If the issue persists, you might want to completely uninstall and then reinstall Office.
Download and install or reinstall Microsoft 365 or Office 2021 on a PC or Mac - Microsoft Support

Microsoft 365 Business Standard Account won't activate Office 365 - Microsoft Community
Fix Outlook account problems in Office 365 for business - Microsoft Support
Set up Microsoft 365 Business Standard with a new or existing domain - Microsoft 365 admin | Microsoft Learn