GORILLA by 00 Seeds

sounds like it may be damping off due to overwatering. take a look at the base of the stem near the soil. do you see any thin weak spots? if so it is damping off which makes the stem weak and hard for the plant to hold itself up. just about all you can do is not water it for a while and let the soil dry out somewhat before watering again. make sure you arent watering super frequently a lot of the time with a young plant like this you can go 3-4 days without watering. I would feel how heavy the plant is after watering and pick up up to feel how heavy it is every day. then when the plant feels pretty light, compared to when it was watered, it is time to water again. watering using this method makes it really easy to prevent overwatering and the issues that come with it.

if it's dry, that could be wilt. If it's heavlily fertilized, it could be too much fertilizer. 3 weeks in solo cup? almost certainly needs a transplant. Did vertical growth stop at some point? Thats a sign the pot is too small. after transplant, give ph'd only irrigation to set the soil/substrate. Wait for a hint of deficiency before fertilizing again and dial back from before. Those look really dark and crispy unless it's just the photo deceiving me. it's possible it's a bit rootbound and that is impacting nutrient uptake too... always easier to add things later... impossible to take things out, so be reactive, not proactive.