Signal has a fascinating blog post from 2017 about how to use Intel's Software Guard Extensions (SGX) to actually let clients confirm that the software they're communicating with is the exact version they expect it to be.

https://signal.org/blog/private-contact-discovery/

SGX is definitely not bulletproof (https://medium.com/@maniacbolts/signal-increases-their-relia...), but it exists to do exactly this job, and Signal is using it.