On my Android phone, I almost exclusively use TTS (text to speech, aka TalkBack) and Google Assistant, in order to not look at the screen. To keep the screen "off", I set the backlight brightness to zero, and run Twilight (a "DC-dimming" app) to make it even darker. But still, I get screenstrain when looking at the (unlocked) screen (although it sets in pretty slowly). The reason is that even with brightness "zero", it's not actually zero.
Is there a way to set the screen brightness to real zero, with some app?
I tried this:
https://play.google.com/store/apps/details?id=io.japp.blackscreen
But it's too easy to turn off - it puts an always-visible "turn app off" button right in the middle of the screen. Which means I'm always at high risk of the screen coming back on unexpectedly.