“Signal is being blocked in Venezuela and Russia. The app is a popular choice for encrypted messaging and people trying to avoid government censorship, and the blocks appear to be part of a crackdown on internal dissent in both countries…”
Matrix doesn’t have encryption as the default
Also Signal doesn’t have any backdoors. I can say that with high certainty as it has been audited more than any other messager.
It doesn’t matter if it is a business entity operating under a government then you can never really know because gag orders. Centralized servers can be blocked. Telegram and Signal apps could have a back door. This is why open stack is important. And not just the code. Also encryption is default for p2p one on one conversations. It’s not in channels by default because it can complicate public use.