Interestingly, I had a very similar issue with my Pixel 3 in the past. The display was just black and it did not responded (I thought). Restarting it displayed

Interestingly, I had a very similar issue with my Pixel 3 in the past. The display was just black and it did not responded (I thought). Restarting it displayed the Google logo and then went black again. I was outside at the time, on a sunny day. I thought about this possibility of low brightness setting, but it was so dark that I could really not see anything (even when covering it with hands, getting in a dark corner somewhere), so I thought it must be some other problem. Later when I was back home, in a dark room, I noticed that I could barely see it again. Then just setting the display brightness higher again fixed it. I'm still not sure though if the brightness was just at the minimal level, and that is just too low outside to see anything, or if it was even lower than usual, similarly as you describe.