What's funny about messaging apps, that offer security, is that if you are using it from a phone in your name, it really doesn't shield much. A lot of people think they are "outsmarting" the federal government, I've known guys that take to Signal or whatever to coordinate something as benign as a QP weed drop out of state, as if
1) Anyone gives a fukk
2) If surveillance was up on you, they wouldn't be able to catch it.
3) The phone is in YOUR NAME
I assume they can, if they want to spend the time and money, check which apps you have downloaded, and subpoena the company to provide the info, and probably intercept the messages in real time.
If you are using an Iphone and backing it up on cloud, like Manafort, I think those messages would transfer.