Growth stopped

What is you humidity and and ppfd ?

Those tiny dots on cotyledons and first true leaves - could be early signs of spider mites.

Light hits topsoil, evaporation dries top couple inches real fast. Gravity pulls water down out of reach of tiny roots. Coco is especially "airy". Water then add a non organic mulch around the plant to slow evaporation, burner liner works well, something white that will help reflect some of the hear off the soil jist until she is big enough.

potting up with appropriately sized pots to plants is absolutely a benefit compared to 'nature'. You will develop a better root zone by doing so. a tiny plant sitting in a saturated pot for 10+ days is no good... same reason you don't leave irrigation water out for 10 days stagnatingn growing weird shit. The plant should drink fast enough to warrant the pot size. if it doesn't, it's a pain in the ass to try to water a smaller volume in a bigger pot.

too much light too soon. Nodes are stacked on top of each other. you may have to reduce light until they start to stretch, then ramp back up to ~35-40 DLI. I second the 'use apporpriate size pots' suggestion too. Large pots and tiny plants is a very bad idea. Even if they are autoflowers. I've never seen a plant stop growing from potting up in 300-400 personal observations. YMMV. Though if someone is shocking plants into non-growth from merely potting up, then they should probably find a new hobby, lol. The pot size could be contributing to the slower above ground growth, if it's focusing on the tap root hitting the bottom. Node spacing is the guide to light intensity... these top-down photos could be deceiving.. but seems like node spacing is very tight. The seed has enough resources to power growth the first 7-10 days or so... but in soilless you should be feeding every irritation.. probably around an overall EC of 1.2-1.5 -- this does not count what is added from your tap water. it is only referencing fertilizer in solution that is applied to the medium. cocoforcannabis.com -- guides and articles, only. Avoid forums.. avoid all forums, lol, until you can effectively discern bullshit from fact. Doesn't have to be coco to use this info. it's great soilless growing information. Coco is meh, imo. 70/30 coco+perlite is convenient, but 50/50 sphagnum peat moss+perlite is better (i'd suggest vermiculite #3 over perlite #2, too, as it adds plant-available silica) Your watering habits need to be fixed to.. can confirm with the guides from the websit above... 1) fully saturate with 10% runoff.. .always with fertilizer. 2) wait for appropriate dryback and repeat. ** in the context of a big pot tiny plant you should water a smaller circle around plant, but do make sure it gets wet all the way down and do make sure you get sufficient runoff. 10% or more runoff is essential to maximizing the benefits of soilless growing. If not doing so, might as well grow in soil. Gonna cause a buildup of nutrients at some point that was completely avoidable.

Hit it with some foliar spray and water it in a fashion that tends to the roots needs. You still might be able to save it

In nature a lot of Seeds die. No water = no root. End. It is just easier in a small one to water it correctly. A big one is ok, too. Just not so easy.

Coco has no nutrients.........are you feeding them? Almost impossible to over water in coco...........water the entire pot until run off........not just in small circles or just next to the plant........roots will not grow into dry areas. Size of pot is fine, no need to start in "mini pots"...........what do people think happens in nature when plants grow in the ground??

There fine those just rooting in now, don't water too much

Maybe only water lightly around the base of the plant(after letting her dry). How far are you from light source? At that stage I keep them pretty close.

the pot is to big. better to start with a mini pot - otherwise it is not so easy to be on point with the watering. The plant is now exploring the root zone - which is large. after getting to the bottom it will start again to grow. (but why there is dirt on your newborn? it could infect the newborn with some fungus or other bad stuff)