Always login to https://portal.office.com directly instead of clicking on any email link to login to your Office 365 Webmail.
Once in your webmail, do check on your mail rules by going to the Gear Icon on the top right corner,
select View all Outlook settings
Select Rules and make sure no email rules that move your important emails into other folders.
Select Sweep and check too
Check Junk email and ensure no important emails address are blocked and those who should be on safe senders and domains should be the ones u trust. Optionaly u can tick on Trust email from my contacts
And lastly ensure under Forwarding there is no unknown emails that u are forwarding to
You are good to go once you are sure that nothing bad is inside these settings.
Follow this link to secure your account with 2FA:
https://helpdesk.ispeed.sg/support/solutions/articles/16000114025-enabling-2fa-for-your-office-365-account