There is a book called the Sunset Western Garden Book that has a chapter on "what to plant beside swimming pools". It is a widely available book and also most every library in California has it. I'd check that list.

Queen Palms are really messy with their fruit, which drops, rots, stinks, and draws clouds of flies. This is true for the cheap, common palms (Queen, Washingtonia) in So Cal. The seeds and fruits also draw rats, and rats love to live in the fronds. Acacias drop a lot of litter--flowers, pollen, leaves, twigs, likely to fly right in your pool.

The standard thing to plant is Italian Cypress that you top when they get to the height you want. You get a dense screen that isn't wide. Topping trees is sort of barbaric, but when you have limited space and need privacy you do what you do, and letting them get too tall isn't a great idea.

A good basic shrub like Ligustrum japonicum will get to 12' fairly quickly and can be sheared into a dense hedge. It's quite clean IF you keep it sheared regularly. Also tough as nails.

Some of the selections of Pittosporum tenuifolium can make good screens with modest litter drop if you keep them sheared regularly. They do not like being away from the coast, so if you are farther than about 8 miles inland, maybe don't use those.

Metrosideros 'Springfire', nice and dense.

Italian Buckthorn.

The gold standard for narrow screens for Southern California used to be Syzygium (Eugenia) paniculata. You can get something 12' tall and 18" wide. However the Eugenia psyllid kind of spoiled the party a decade or so ago. I'm having decent success with mine as a tiny predator of the psyllid has been released and established in the area.

At 12 feet tall, a medium shrub is all you need.

Avoid Ficus as it cracks retaining walls, pool decks and pools.

Podocarpus makes a gorgeous screen, but eventually the roots will also destroy concrete structures. It just takes longer than Ficus.