Last update from Microsoft Support:
"…
I'd like to provide you with an update on the situation. After checking with my team as well as my advisor, the New Outlook is a recently introduced feature, and the Microsoft team is actively engaged in refining and enhancing its functionality. As you may have observed from the link you shared, it appears that several users are experiencing similar issues.
Please be assured that we are fully aware of these challenges and are dedicated to addressing them. In the interim, we recommend utilizing the normal Outlook, which remains a reliable alternative. We understand the value of the advanced benefits that the New Outlook brings, and we share your enthusiasm for its potential.
Regrettably, at this time, the development of the New Outlook is not progressing as swiftly as we had anticipated. We acknowledge the limitations it may currently pose, and we ask for your understanding as we invest the necessary time to improve and refine the experience.
Rest assured that our team is diligently working to enhance the New Outlook, and we are committed to keeping you informed about its progress. Once we have completed the development and improvements, we will promptly announce its availability for users.
…"
Summing up, it's recommended to utilize "normal Outlook" at the moment and wait for their solution. New Outlook is not something we pay for and have a right to demand an immediate solution. It's more like a beta version so it might be reasonable to stay with old mail client for now or utilize the workaround for 15 USD (or 14 EUR) I suggested above.