> every app installed is known to the proxy since each app has a unqiue key

GrapheneOSs proxies do not collect and send any "unique keys" from apps. That is made up.

> They mention no proxy of RCS data, but in theory, an RCS message requires location data. So, the proxy knows when a message is sent and received, at a minimum.

They dont mention a proxy of RCS data because there isnt one. RCS messages do not require location data. None of the GrapheneOS proxies are related to RCS and the proxies do not know if an RCS message is received or sent.

> So, based purely on the FAQ, if you use the sandboxed services and enable RCS, Graphene knows every app you install and has your location data, but they erase it after a couple of weeks.

You did not read the FAQ at all.

> There is some vagueness regarding the RCS implementation message content. People claim Google can't read it, yet they specify they can read it in the client terms, and offer a managed RCS archiving service that works regardless of messaging client or supposed encryption. Is the RCS query proxied? Graphene does not mention it, but the simultaneous location data to use it is.

RCS is end to end encrypted on Google messages. The RCS spec also includes end to end encryption. There is no RCS proxy and RCS is handled by google messages. No other client for it exists at this time. The location data provided by SUPL is not given to apps, it is used for OS location that can be reported to apps. An app must have the location permission to have location data provided by the OS.