I wouldn't be surprised to find out that it has been decrypted

I don't think we need this sort of fear-mongering. Signal's encryption is fully open source, it has been vetted by cryptographers far more experienced with this stuff than you or I. They even introduced, a few years back, an encryption algorithm that's future-proof against quantum computing.

All you are doing is potentially pushing people away from one of the few known-safe options. That's the opposite of helpful.