I can't add anything to this. Though at least in your picture, I don't see any evidence of insect pests.

https://ourgardenworks.com/basil-leaves-turn-brown/

Possibly the beginning of Basil Downy Mildew.

It looks like you have wood mulch under this plant. two thoughts:

1. there is something in the wood that is affecting the plants, maybe stealing the nutrients;
2. the water isn't getting to the ground, but rather being soaked up by the wood... I've had this happen.

I'd pull wood out from around the plants and use something else as mulch, maybe hay or straw.

Fertilize the plants themselves... and make sure they are getting water.

@CA Kate z9 Thanks. It looks like wood mulch but is actually a layer of raised bed soil that I used to top off this and another bed. It is a different mix than I typically use and quite frankly I'm not happy with it given the amount of wood and other large chunks of material. It seems to dry out much quicker than the soil I normally use and I suspect that is a major part of the problem. I'm going to fertilize and thoroughly water over the next few days and see if it improves.

Wood actually in the soil will steal nitrogen. Fertilizer with something a little higher in Nitrogen... and maybe more often.