I don’t know what would fit your needs, but Signal does not require Play Services. And even if those are present, it does not leak data to Google. Other than “Signal is installed” and “You get a push message”, Signal does not put your messages into the notifications. Instead Signal connects to the Signal servers and then gets the encrypted messages from there and only then decrypts.
Even if you have Play Services installed, you can force it to use a background connection inatead, if you disable Play Services before installing Signal, it wall automatically fall back to it.
If you want a version without Play Services libraries, you could use Molly, a hardened version of Signal, which is available in a version without those libraries.
Molly even allows linking phones as secondary devices, not just desktops.
A bunch of marketing blah blah, I wonder what they’re up to.