This is pure speculation and not practical advice, but if you were trying to get in to your accounts from a 'starting from nothing' situation, I wonder if you could get a passport etc. and then make a GDPR request for your data from google?
Obviously you wouldn't be able to get in to your account to use google's built in tools because you wouldn't have access, but if you sent a letter to their legal team with proof of your identity then they would be obliged to process the request by law (as I understand it).
This might (should) get you your data but that data won't include your passwords which (presuming basic competence) Google doesn't store. This means that you are still locked out of many things. The data might also not be in a format useful to laymen and will probably be incomplete in some way, e.g. excluding data you had access to with that account but isn't your in Google's opinon data like shared documents.
Google would need to know that remus@gmail.com belonged to the person making the GDPR request, or it would be an attack vector. From the providers point of view, you are asking for a copy of your data and data about you, and they are not going to give out data that might be yours. Maybe if you had linked a phone number, but even that is arguable.
Obviously you wouldn't be able to get in to your account to use google's built in tools because you wouldn't have access, but if you sent a letter to their legal team with proof of your identity then they would be obliged to process the request by law (as I understand it).