opticalcarrier Is it just not possible with dd?
No, because everything is encrypted: https://grapheneos.org/faq#encryption. Even if it were possible, it's not possible to get the required keys from the secure element.
Still, the only way to get reliable backups is to have a new, modern backup app. Seedvault uses a depreciated or discontinued (not sure which) backup api, so it's not supported by most apps.
As matchboxbananasynergy said above, there are plans to replace Seedvault.