Governments, if they want, can decrypt any chat
This is not true. Encryption that is not breakable by anyone - including governments - and the tools to use it have been available to everyone for decades now.
It might be broken later (which is why the US stores encrypted messages) but not right now, and is unlikely to be in the foreseeable future.
What you wrote is science fiction, not fact. So are practical quantum computers, thus far.
It also ignores the fact that quantum computing would do shit all against symmetric encryption (though admittedly that’s less relevant for whatsapp, but it’s perfectly relevant if you want to exchange secure messages with someone you met physically prior); as well as the fact quantum-resistant encryption algorithms such as NTRU already exist and are already considered for implementation in free software tools (the only reason they aren’t is they’re far less tested and nobody trusts them yet against conventional attacks).