yellow on tip of leaf

Listen to these folks. Gotta re-pot! Tape that cup up for darkness at a minimum and make sure your humidity is +45% (closer to 55-60 if you can!)

4 weeks in a tiny pot is a long time. They aren’t really growing at expected rate. I would always plant autos in their final pots and just be careful not to overwater them. But it looks like you are doing an indoor sunlight tiny pot first time grow? Don’t expect them to come to much then sorry. Get a tent, some lights, an extractor fan and 2-5 gallon pots. Plant more seeds. Autos are a sprint race. They are easy and fast. But you don’t have time to waste on them. Watch this site. That is where I picked up most if my small skills.

I think its rootbound so hot soil and high pH are likely. Also wrap something around the cup so the roots arent exposed to light.