Hard to see from the pic.
Is there anything on the underside of the leaf? Perhaps a pest.
Did you happen to have gotten water on the leaf previously? Perhaps some leaf burn from nutrient, etc. Avoid getting leaves wet unless explicitly doing a folier treatment, etc.
Growing is mostly about learning to get out of the way of the plants, I think. I have made the mistake of obsessing over plants, checking on them constantly, trying to make adjustments in real time. I mostly killed them, even if some got to harvest.
It was almost disappointing at first if I came back from a couple days away to see that they were thriving. Now I think I've learned that all I can do is guide and maintain certain conditions and let the plants do the rest.
To each their own, but I'm doing living soil in SIPs. I've never done so little work nor gotten such good results.