I'm not in the android rooting / modding scene anymore, but isn't there just a way to install a (Magisk?) module or something to spoof the Safetynet check anymore? I'm not saying that is a great idea, just in my memory theres workaround for this kinda thing.
Not possible, you have to run a OS signed by Google.
There are two different Safetynet check levels. One (BasicIntegrity) is easily spoofable, bug GrapheneOS already passes that. The other requires Google certification.