OP asked:

How can you grant access to an account to write remotely, but also protect the data from this account?

So I was thinking that the account should not be able to delete the filesystem in an unrecoverable way. Like overriding the current fs with random data or an encrypted fs and filling it etc.

Like I said on a Hetzner storage box, multiple users get access to the same system, but each one only has file editing commands, not fs editing and they can only access their assigned directory. So if the system does scheduled snapshots, there is no way for a user to delete the files beyond recoverability.