I switched to gOS on a pixel 6 pro a couple weeks ago, got RCS working with the 242499063 version from Aurora and allowing READ_DEVICE_IDENTIFIER. It's been off randomly every few days since but would come back if I uninstalled and reinstalled, but ever since the most recent gOS update to 2025090800, reinstalling no longer helps.
As a data point, I did try moving my sim card (AT&T) back to my old phone (Samsung S22), and RCS connected immediately. So whatever the issue is, it does seem to be gOS related.