I'm interested in finding this out too. Based on reports, this has not rolled out to everyone yet. Some people have reported (on stock OS) having a satellite option under their SIM settings, while others, including my friend running stock OS on T-Mobile, do not have any such option (yet).
Has anyone seen such an option on GrapheneOS? Would such an option ever appear on GrapheneOS? Ideally, has anyone had it working on stock and then switched to GrapheneOS? That would be the best test.