/e/
@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.
@blacklight447 Yes all those measures you mention are important to take for proper data hygiene. However I see ephemeral messages as a "defense in depth" strategy which is more concerned about future use and access to the encrypted data. In 50 years your olm encrypted messages may be easily brute force decrypted. If they are archived somewhere in a server backup or intelligence agency repository those messages could be decrypted.
@supernova to be fair, they are more likely to be intercepted during transit for later decryption, then downloaded from my device.
@blacklight447 If that is your threat vector then yes ephemeral messages won't help, that is not what they are designed to protect.