App can have internal keyword check that could open backdoor to law enforcement when certain terms are said. *fbi enters the conversation* probably won't be in your chat log anytime soon but you can't argue telegram, signal and whatsapp can't do it. Whatsapp being fbs darling almost certainly does already and signal servers anti spam folder is smelling mighty like a five eyes backdoor.

Tbh given both those apps company's have dealings with gov in aus I'm gonna say signals probably already got a backdoor into em. If you don't think so you don't know aus law well enough or who signals are.

Also the owners of the apps aren't liable for the content of the conversations. Their liable for providing a platform for the conversation to take place and for not knowingly taking available efforts to curb criminal activity on that platfor/service. It's like hey I'm gonna rent you a store house to hide all your illegal drugs in Mr gang member. I'm not doing the hiding or anything but I'm assisting the activity by providing the store house. I could make efforts to curb such activity like you know doing a rental inspection once every six months but I choose not to and turn a blind eye. Am I assisting a crime or am I completely innocent? Now repeat this but telegram is the store house.