It's not already disabled, but it will be happening. From the horse's mouth: https://signal.org/blog/sms-removal-android/

Having an alternative that isn't taking this step released before they actually do that change over seems prudent.

As soon as I got that warning about losing SMS support, I disabled updates. That was months ago. For the sake of getting this thing put together quickly, I forked from the latest version that was compatible with the version that was on my phone when I disabled updates. That will be rectified in due time, but I'm pretty busy with life right now.

You're only an automatic update away from losing it. Hence why I suggested locking the version now until you find out what the last version with SMS support was, before transitioning to a fork.