Hi, I'm John! I will help you with this.
Can you please check if your Outlook (Attachments) storage is full?
If your mailbox is near or over the storage limit, new emails might not arrive in your inbox https://onedrive.live.com/managestorage in the same page, please check your OneDrive storage as it's linked to your Microsoft account and can sometimes affect email services if it's full.
Click "Add comment" to let me know.
Regards,
John J.D.