“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…”
Signal has strong cryptographic protocols that are not easily broken. It pioneered the use of double ratchet encryption. (Different keys for each message)
It does expose phone numbers to Signal and the US government but that may or may no be a concern depending on what your threat model is.