how to remove potential harmful pop-up app(s) connected to my Microsoft account?

1. Change the Microsoft account password and update security settings on the Security settings page. Also remove all trusted devices there.
2. Check recent sign-ins on the Recent activity page. Review the last 30 days and mark any sign-in that was not recognized.
3. Review app access and remove anything not recognized. The accepted Microsoft Q&A guidance for compromised Outlook/Hotmail accounts says to review app access and delete any app that was not granted intentionally.
4. In Outlook on the web, check for mailbox changes that attackers commonly add:
   • Settings > Mail > Rules: delete rules that were not created intentionally.
   • Settings > Mail > Forwarding and IMAP: remove unknown forwarding addresses.
   • Settings > Mail > Junk: remove unknown safe senders or blocked entries.
   • Conditional formatting: remove anything suspicious.
5. Review account aliases and devices:
   • In the Microsoft account site, go to Your info > Sign-in preferences and remove aliases that are not recognized.
   • In Devices, remove devices that are not recognized.
6. Turn on two-step verification.
7. If the alert may be related to unwanted software on the PC, turn on potentially unwanted app blocking in Windows Security:
   • Start > Settings > Update & Security > Windows Security > App & browser control > Reputation-based protection settings
   • Turn on potentially unwanted app blocking and enable both Block apps and Block downloads.
8. If Windows Security already detected a potentially unwanted app, open the notification, go to Virus & threat protection, select the detected item, choose the action, and then select Start actions. Until an action is selected, the app is blocked but not removed.
9. If access to the account is still in question, use the Microsoft account recovery help or contact support.

References:

• Check the recent sign-in activity for your Microsoft account
• What happens if there's an unusual sign-in to your account
• How to recover a hacked or compromised Microsoft account
• Protect your PC from potentially unwanted applications
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