Someone in that thread notes that when you install the Signal APK from here [1] it "doesn’t get updates tho", but this isn't the case. Signal will update itself; you get a notification to update. Often earlier than the Play Store, probably due to its reputation to randomly delay updates.

[1] https://signal.org/android/apk/

Yeah. Installed Signal as raw apk in GrapheneOS and you just need to open it to install the update. It does not update automatically in background. But anyway, works.

Yes, it notifies of updates (once it did wake me up in the middle of the night), but last time I checked, it does not update itself automatically. Obtanium works, though, but a bigger issue is the extreme power drainage of the websocket.

Signal sends you a notification that says "new version available, tap here to update", but tapping it never did anything for me. I have to re-download the apk their website every time there is an update.