Interesting, that is good to hear about Molly-FOSS. I read a recent post about some people saying it is taking between 20-70% of their battery life: https://discuss.grapheneos.org/d/8976-signal-vs-molly-vs-molly-foss/86
My understand is that signing into a google app, like google voice, on AOSP is like signing in at a system level (sorry if that is not correct terminology). But essentially, that sign on information would be shared system wide amongst google apps such as google play services. Perhaps I am wrong in this understanding though.