Most deserts are actually formed primarily due to abiotic features like geography. Usually if you see a desert, there's a nearby mountain range that that desert is in the shadow of, preventing it from getting much precipitation

You're not wrong about the diminished abilities of a desert to hold water. More people drown in deserts every year than die of thirst. When it does rain it pools up and can easily create flash floods. The major problem is if you do try to start building any topsoil, these types of floods can wash away your years of work. It's a hard problem because you're both in desperate need of precipitation and desperate fear of it

Techniques that could be used to combat this are things like the waffle gardens[0] that Zuni people have used for a long time, olla pot irrigation that have been in use in China and Northern Africa for over 4,000 years, and complex swale systems, or terracing systems like the Incans used to basically turn deserts into fertile ground[2] and might be the reason we today have potatoes, tomatoes, corn, beans, peanuts, sweet potatoes and a large number of other crops domesticated in the Andes

I really think the biggest challenge is just shade though. The worst thing you could possibly do for soil is expose it to direct sunlight. One "geoengineer-y" idea I toy with that keeps coming up for me is what if we just built a bunch of large boxes made of wood or bamboo some other biodegradable material and just left them in the desert. All that you really need is something like the structures that shade covered parking lots. If you just make some large, flat, cheap structures like these you'd be able to provide what's possibly one of the most valuable resources in the desert: shade. Ultimately if you manage to start a soil ecology up, the whole issue solves itself. Soils inoculated with mycorrhizal fungi hold 50x as much water as those that don't; the soil activity of bacteria, fungi, protozoa, nematodes, etc also turn the large grained sandy soils into more loam-y soils that can support many more life forms and plants; the fine roots of plants that tend to grow in soils like these hold together soil better so less topsoil gets lost; plants that grow with mycorrhizal fungi are less susceptible to drought (as well as frost and basically every other stressors you can think of) and have much more access to nutrients.

Basically all our problems go away if we can just get soil going. And plenty of desert plants already know this. Creosote bushes, nara melons, and the nitre bush are 3 examples that immediately come to mind. All of these slow growing plants have the strategy of simply providing shade and holding as much soil together as they can. And over time an incredible diversity of soil microbiomes form around the roots of these plants. The nitre bush also forms nabkhas[3] that capture other debris flying around and over time lessons the harshness of the desert winds, thereby lessening the rate of topsoil loss.

Nature already has solutions. If we could just kickstart the process by providing the right microclimates we might be able to help these organisms stand a chance against the forces of desertification

[0] https://www.notechmagazine.com/2021/11/waffle-gardens.html

[1] https://www.nativeseeds.org/blogs/blog-news/how-to-use-olla-...

[2] https://www.mayaincaaztec.com/inca/incaagriculture

[3] https://en.wikipedia.org/wiki/Nabkha