I want them to have the clear objective of making money. That gives they consumer some control as you can just not give them money. That still can be true for non profits but it isn't as powerful.
Proton AG will still need to be financially feasible. That is not changing. You can still not give them money if youd wish. They just have backed up their mission statement with actions instead of just words.
You say that as if companies haven't been imposing greedflation/shitflation on everyone for many years.
Voting with your wallet isn't an effective means by which to motivate a company to do anything. You're just a drop in the bucket, so your distaste for a company will never influence their behavior. You know what does? Shareholders.
Thankfully, Proton is moving away from that harmful influence by becoming a non-profit, so that will be less of an issue for them and they can focus on delivering services that users actually want instead of shoveling in anti-features and forcing arbitrary price-hikes on their customers like most for-profit companies do.
This. The best you can do is encrypt your messages locally before sending. But then your email service provider still knows where you are, when and to whom you are sending the message to, and how long is it. And so does the recepient's email provider and anyone in between. Best they can do is to promise not to keep that data. But it's just that - a promise, which there is no way to verify.