Marie I chose my words poorly. All of out group chats are in Google Chat, because it's cross-platform. Switching to Signal wouldn't exactly lose them their histories, but it would demarcate them such that every old message would be on Google Chat and all new ones would be on Signal. And most of my friends won't switch. Which leaves the option of not using GChat at all. Which would mean that each friend needs to send their messages to GChat for everyone else and to Signal just for me. Which they won't do, because they won't install it.
As for APK Pure, it crashes on my phone. Not sure why. I'm on a fully up to date instance of GrapheneOS on a Pixel 8 Pro, but it crashes as soon as it starts up. So I just downloaded Google Chat straight from the APK Pure page itself, but Graphene tells me it can't parse the package.
As for Aurora, I use a dummy Google account for all downloads. I don't mind having the account, but I want to severely limit the data Google is able to collect from me. But without Play Services GChat will open and run, but it's impossible to sign in. Unless there's a work-around for that that I don't know.
What I'm really looking for is a unified, stand alone, messaging app. Remember in the early 2000s when there were apps that let you sign into AIM, ICQ, and whatever else was being used at the time and funneled them all into one interface. I just want something that I can actually sign into without Play Services.