PAX
Whenever you have more time, I recommend watching the videos on the Poultry Keepers 360 channel, especially the ones with Jeff Mattocks: https://www.youtube.com/@poultrykeepers360/featured
They have a series of livestreams, "Shining Light on Common Chick Health Problems", it's great, goes thru the different illnesses, and the second in the series is about poop:
I recommend watching them even if you don't have chicks, because any chicken is susceptible to almost any of these problems.
I had a chick die from something similar to what you're going thru, with hanging head and gasping. Soon after I found Poultry Keepers 360 and took their advice, my flock's health has improved since then.