You can disable updates. As long as the servers (and the OS) don’t break compatibility, you can continue to use the same old likely-non-backdoored version.
At least when downloading from the Play store, Google requires the application be updated every 90 days or so. I've run into this multiple times where the application ceases to function after the 90 day window until I go update.
Not for Signal. I was periodically prompted to update with the warning that I would lose access to signal if I didn't. Then I upgraded and they robbed me of SMS features. I would have been happy to remain on a previous version.