Using the New Outlook for Mac for personal email and calendar
You are not the only reporting this issue from the last few days.
I don't think this is something you can fix on your end. I fear Microsoft has to fix it for us.
Please make sure you submit feedback to report this issue. As a member of the community forum, we cannot escalate this to engineers but your feedback will reach them.
Please follow the instructions and template created by hornblower here to report the issue