Balcony Auto Gelato with Yellow and Brown Leaves

Hey mate. Looks fine to me. The bottom ones normally yellow off anyway, the top ones are nice and green. It’s small though for 3 1/2 weeks old, maybe not getting enough direct sun on the balcony?? Or cold nights?

I don't think you have anything to worry about here, personally. Your issues are with the very first leaves which can always go a little wonky - and since the dark spots are not occuring on the newer growth, perhaps they were caused by some water or nutes being dropped on them and burning them... the lowest leaf may have been touching the soil for a while as well. And the cotyledon's life is over... the job they have to do is done and there is nothing more for them to do... To me, your plant looks absolutely great - I'd snip off that lowest leaf if it bothers you to look at it - and relax.... you're doing great! Good luck.

Easiest way to know young and vegging plants, if their getting enough feed or they need a little feed., is to watch the stems of the leaves. If their nice and green the way I see in your last pic, they do not need an increase in feed. If you see some red coming into the stems of the leaves, then their needing a little increase in feed. This only apples to vegging plants., not blooming plants. Cheers