Could you please elaborate? I wouldn't think this causes an issue unless they need to link against it, which I don't think they do.
Go read the GPLv3 license and/or ask yourself how Linux distributions are able to ship a mix of GPLv3, v2, MIT, BSD, etc licensed software all in the same image.
GrapheneOS may or may not have a policy against shipping GPLv3 software (I don't know), but if they do, it's a political or business decision, not a restriction imposed by GPLv3.
The GPLv3 only applies to a work and works derived from it, so either if you take an existing GPLv3 project and modify it or if you link against a GPLv3 project. In these cases, the other code needs to be under licenses that are compatible with the GPLv3.
This is clearly described in the GPLv3:
A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.