Interesting, just inferring from that it sounds like GrapheneOS's actual-security features might have been tripping up PayPal's root-detection "security" features.
(Rather than something fundamentally incompatible, like them using Play Integrity)
(Rather than something fundamentally incompatible, like them using Play Integrity)
IMO headline is very misleading, and OP should have tried disabling all exploit protection options before jumping to any conclusions. PayPal isn't actively trying to block GrapheneOS as of now.
It reduces security of the app itself, but doesn't affect security of the phone by much.