> T2B3.230109.009.2023031500 (Pixel 6, Pixel 6 Pro, Pixel 6a) — 2023-03-05 Android patch level but only 2023-03-01 Pixel patch until a March stock OS release is published with updated firmware, etc. (marked as 2023-03-01 overall patch level in the OS)

Your baseband isn't protected. GrapheneOS patched Android, but the complete device set of images (firmware) is still vulnerable. That said, GrapheneOS does seem to implement its own additional baseband hardening.