The operating system is not the only way of spying, there is already firmware on your device running without your permission, pretty much impossible to see what code its running, and requires expert level knowledge to disable (or tamper with :)) if a third-party firmware implementation that allows disabling the IME doesn’t support your device.

Most phones today also just have a non-unlockable bootloader with a spyware Android skin installed. Locking something down to this level is not really impossible.

First of all: You don’t need end-to-end encryption for e-mail. Don’t choose something like Proton or Tuta just because of that (I highly recommend reading the linked reviews).

Disroot seems to be the only e-mail service which fits your criteria (though screen reader support will depend on what e-mail client you use I guess, not sure about Disroot’s webmail in this case but since it allows free accounts you can test it out for yourself.)

You can use OnionShare to host a chat instance on the Web over Tor.