Mail banner notifications not working in Mac Mail on Mac OS Catalina

Hi

I have 3 different IMAP mail accounts in my Mac Mail program (version 13.0)

When a new mail arrives I do hear the sound of new mails, but I do not get the banner notification.

I tried several options already.

• do not disturb is not enabled
• tried different settings of the banners in the notification centre

My wife has an email address from the same IMAP server on her new MacBook Air 2019 and does get the banner notifications. So it's not server related.

Who can help me solve this?