Maybe it's outgrowing your container? Basil grows fairly large roots, and the discoloration on lower leaves could be nutrient deficiency. This article has some good info on container sizes: https://yourindoorherbs.com/what-is-the-best-container-size-for-your-indoor-basil/

Might also be a good idea to pick that giant leaf, free up some resources for the rest of the plant.

Thanks so much! That's. Good point about the large leaves. They didn't look rootbound to me, but I do have soil and I've been meaning to pick up larger pots. Going to do that today. I don't know if you are able to look at my other posts I made... I think my zuchini and watermelon may have mosaic virus. In which case I need to throw them out. I don't think anyone responded on my other posts yet. Maybe you're knowledgable regarding those as well. I would appreciate a second set of eyes and thoughts.

Unfortunately that's all I've got, sorry! You could try reaching a wider audience by adding more tags, I usually include Container Gardening and there are a few plant-specific ones as well. I've also had good luck searching for old threads using "site:houzz.com" on Google, e.g. https://www.google.com/search?q=site:houzz.com+mosaic+virus&source=hp&oq=site:houzz.com+mosaic+virus

Good luck!

The large leaf is making resources for the plant, not using them. Don't remove it, or any leaves, unless you're wanting to use them in the kitchen. But do put it in a larger pot. Look under the damaged leaf. Any small insect pests?

I stand corrected, thanks floral_uk! I've been doing it wrong this whole time, though the Aerogarden I grow mine in is very forgiving. More info on pruning here: https://www.ruralsprout.com/prune-basil/

Personally, I don’t really think of it as pruning so much as harvesting. The pinching which makes a plant bushier isn’t unique to Basil, it’s used on many plants. But you can’t make pesto out of petunias. 😉