your gpg example removes the deniability since it proves who wrote the message.You confuse digitally signing a message with the sender's private key, and encrypting a message with the recipient's public key.
A shared secret implies that the message was sent by someone who knows the shared secret, and that restrict the number of potential senders.If you mail a message with gpg, everyone knows the public key, and the message is still safe.
The knowledge of a shared secret suggests that the message could be authentic. It makes more sense to use asymmetric encryptions (without signatures).
Proton's CEO comments on Trump: https://medium.com/@ovenplayer/does-proton-really-support-trump-a-deeper-analysis-and-surprising-findings-aed4fee4305eI use Proton and I'm happy with it. Tuta seems a great option but it's less complete if you need the full package.I recommend to buy your own domain.
Same Here: 2FAS. If you are into coding, you can also write your own: there are lots of libraries to do the cryptography for you.
The hardest part is to have your mail sent directly to your domain, skipping Google entirely. It’s such a painful process!I started with a passive-aggressive strategy delaying replies to who still uses gmail: “apologies, I rarely use gmail these days…”
“In the end, you’re measured not by how much you undertake but by what you finally accomplish.” - Trump