Since we cannot verify the software they run on the server is the software that is open source then we must assume it is not.
But that’s like, the case for pretty much every messenger out there, outside of self-hosting, which will not be done by 99.99% of the general population.
The onion:
Dying Gazans Criticized For Not Using Last Words To Condemn Hamas
https://theonion.com/dying-gazans-criticized-for-not-using-last-words-to-con-1850925657/