The AADSTS51004 is an error message code that happens when a user account does not exist in a specific directory. Based on your description, you got deleted from the tenant. It could also be that you need to be invited again
Since the school has changed the domain, I would recommend you contact the IT department. They could restore access to your previous account associated with the old domain or help you migrate to a new account under the updated domain or your personal email.
+if you recieved an email on your personal account another possibility may be that you simply just try and sign in from your personal mail via an incognito tab first.
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Regards,
Abiola