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It is slugs. They LOVE basil and only come out at night, so it often appears that the holes mysteriously appear. The damage can then cause yellowing.

This article will help:
https://www.gardeningknowhow.com/plant-problems/pests/facts-about-slugs-and-how-to-kill-garden-slugs.htm

Without knowing what kind of plants you have, where you live, how often you water, etc., it is hard to provide help. I can say that we have had unusually hot weather in Dallas and anything in a pot, requires watering a minimum of once a day and preferably two. Plants like petunias have been pulled and replaced with plants that can better handle heat and less water. Sometimes giving certain annuals a haircut and providing good fertilization and water will lead to new plant growth but I don't even try that this time of year and with as much browning as you describe. Not only are they ugly but producing new growth while just trying to stay alive is asking a lot.

This article should be of help to you:

https://www.gardeningknowhow.com/edible/herbs/basil/basil-diseases.htm

Frequent harvesting will help to keep them from bolting. Even if you don't plan on eating it right them, basil freezes well, so harvest as much as you can. If in pots, water 2 times a day to help keep the soil cool. Hot soil encourages flowering. I have even known people to place 1-2 ice cubes on top of the soil to cool it down some.

There are several different insect pests that like basil, neem oil is a good way to control the problem. This article should also help:

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

This article should help: https://www.gardeningknowhow.com/edible/herbs/hgen/how-to-dry-herbs-various-methods.htm