@supernova wouldnt take "epheremal messages" as anything serious.
nothing stops the other party from making a screen or taking a picture of the screen, its security snakeoil.
all i could help with is keeping your phone clean, and being sure that the chat is gone on your own device in the case it gets seized at a later point in time. Also you need to make sure it gets propperly scrubbed instead of just being "deleted" in the tradional meaning.
@supernova it is snake oil, once it leaves your device, its out of your controll, how do you know the other party uses a modifed client that doesnt delete the message or exports everything, how do we know the other party hasnt made a screenshot or taken a picture of the message? Ephermal messages should only be used for data hygiene on your own device, if you cannot trust the other party, ephermal messages wont help you.