As I read your post, you're referring to an Outlook.com account, rather than to using Outlook for Windows to access your emails. (I really hate the way that Microsoft keep using the same name for entirely different things. It can lead to a lot of confusion!). The problem you're experiencing doesn't seem to be one that Microsoft is currently aware of, other than for users of Firefox with certain extensions:
https://support.microsoft.com/en-us/office/fixes-or-workarounds-for-recent-issues-on-outlook-com-8c95d913-d96b-4065-9171-e1fa44b03ff5
All I can suggest until they fix the problem is to try using a decent email client (such as Thunderbird), rather than using the Outlook.com website. [Webmail is only ever a 'second best' way to use email anyway]. At least then you won't miss any important incoming mail.