Actually, this is maybe a better video I made of some other seedlings:
The biology also didn’t work out for me. Apparently, the non-gravel substrate works better so far. I just thought I could get a clearer image and capture the entire seedling tray. And I expected many more seeds to germinate, making everything green. I have to rethink now if I want to use fine grey sand and oversow the seedling tray, and zoom in, for a new try. But I need to fix this hazy image problem first.