I made one of these ESP8266-based clocks[1], which has a little web UI to configure it, including the brightness of the LEDs. I commented out some of the code (Octoprint, Bitcoin etc.) since I wanted it to be a simple as possible. Even at the lowest brightness the LED matrix can do I found it too bright for my bedroom, but covering it with a thick sheet of paper worked well, in daylight you can't see it's on at all (which is fine, I am not looking at it), at night it's just readable enough.

1: https://www.instructables.com/LED-Marquee-Scroller-Wemos-D1-...

FWIW you could probably just recompile with a lower brightness

Edit: nvm, just reread and saw the rotary encoder. So no need to recompile!