I use Protonmail as they offer quite a bit of privacy, offer lots of features, and are free. I particularly like that they protect from tracking pixels notifying the sender you read their email.
I don't know if it'll ever "get there" because they've not demonstrated that they're putting in any effort at all. It's currently on version 3.0.16. According to ApkMirror, they released 3.0.1 in June of 2022. So that's over a year of "stability improvements and bug fixes". Meanwhile they launched Proton Pass, Proton captcha, desktop clients for Drive, introducing new plans, etc.
Honestly, I just want threaded conversations on mobile.
Indeed, same here but while using my own domain name, this way if some day, for whatever reason, either they go "bad" or I find "better" I can switch without much worry.