Hello Tolas E,
Thank you for reaching out to the Microsoft Community. My name is Gunasekar and I'm happy to help.
By default when you no longer have the Mobile device or Authenticator app to confirm, you will have other options to confirm your identity (i.e.) using your alternate email address or Phone number.
For e.g. see image 1
(or) if you have already backed up your account credentials to cloud, You can recover your account credentials from your cloud account.
https://support.microsoft.com/help/bb939936-7a8d-4e88-bc43-49bc1a700a40
Also, please note that depending upon the type of account is affected, (outlook.com account, Hotmail account, or professional/educational account) the recovery process may vary. For educational or Organization accounts, you can reach out to the IT administrator to change the MFA.
If it is a personal account, check if you have any other options to sign in to your account.
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I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,
Gunasekar N