JTL pretty old, but they play audible books and have a little web browser.

    a year later

    I tested on LedEyeStrain group in Telegram the Kindle screen.
    No pwm, but High modulation.

    So use Kindle with an external light

    I don't use Kindles but I have often had firmware updates ruin previously working devices.

    Check on xda-dev's, sometime there are ways to hack the device and restore older firmware (I was able to rescue a Fire Stick this way)

    dev