d9780 It's generally a good habit to scrutinize all runtime permissions.
Sandboxed Google Play doesn't come with any standard runtime permissions (as compared to stock). If you had installed a couple of messaging apps, to take a commonplace example, in the same profile as Sandboxed Google Play, they can detect it and use it (eg. to grab the SMS verification code without their app needing the SMS permission).
If you don't scrutinize these and similar permissions (for example, by denying them and seeing is you can input code manually), Play services on your GrapheneOS device can accumulate a whole host of them. This is how you end with 'leaks' above. These Play services permissions can often be bypassed. You won't see them on regular Android devices with GMS because they start out with all the standard runtime permissions granted.