Managing personal Outlook.com account settings, security, and privacy
Hi,
Like I suspected, the issue was not locally. Microsoft blocked my account because of login attemps from other places (not me).
I was able to request to unblock the account via https://microsoft.com/nl-nl/concern/accountreinstatement (if you are not in The Netherlands, check for the country code in the URL). Between 24-72 hours they processed the request and now my account is unlocked again.
I use my personal account for many years and never had this before. I'm not sure what can be done to prevent this the next time, as it was caused by an external factor.
Thanks for the help anyway! :)