Thank you for posting this in Microsoft Q&A.
I understand that you are unable to login to Microsoft 365 account because 2fa is enabled and my old phone with authenticator app is not accessible.
Please reach out to the support team to resolve your issue.
You can look into below article to get support numbers depending on your country: https://learn.microsoft.com/en-us/microsoft-365/admin/support-contact-info?view=o365-worldwide
or creating a ticket through a different account: https://learn.microsoft.com/en-us/microsoft-365/admin/get-help-support?view=o365-worldwide#phone-support
Hope this helps. Do let us know if you any further queries.
Thanks,
Navya.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful. And, if you have any further query do let us know.