Theoretically, yes. But if it’s a legal entity that added it, they can easily circumvent any attempt to eradicate it. Or, in a more extreme way, criminalize FOSS chat apps altogether, then the code will have to be analyzed in a RE environment. Maybe the non FOSS server code is where the backdoor is added. There are so many relatively hidden ways to compromise a chat app’s supply chain.
I agree with you. I just think “they” will take that fact and just sit with it. I think “they” will do everything they can to get multiple backdoors in there (and I use the term ‘backdoor’ loosely to mean anything that can programmatically circumvent the encryption). There are more of them, in terms of power and funding, than there are of us. They will eventually succeed, if only for short times each interval. That’s why I wrote that the solution is a chat revolution. I don’t know what that will look like, but we need something they can’t successfully attack.