Swimming Pool Repair Oversimplified

One answer: "3M 5200 Marine Sealant/Adhesive". This stuff sticks to everything, stays elastic, stays waterproof, doesn't care about thermal expansion or anything else. It patches cracks and bonds tiles that nothing else will.

In this photo my sister Kathleen uses her ballet skills to assist her husband Dave. He's glueing tiles back onto their pool and sealing the expansion joint under them.

My sister and brother-in-law had finally gotten their castle almost perfect. Every hurricane season the whole neighborhood blew into their pool and they had to buy all new trees, but that's just life in Florida. The real problem was the pool. One row of tiles was located right over the expansion joint between the pool basin and the patio slab. Various shades of off-white grout beneath the tiles revealed the previous owner's fruitless attempts to graft them back on.

I was visiting for a few days on my way to live in a swamp for a few months. Kathleen has two simple rules for me when I visit. 1). "Don't touch anything". and 2). "Don't do anything."
That minimizes the amount of time she has to spend walking around the neighborhood apologizing to everyone.

I happened to arrive just at the same time as the Pool Guy. I was driving the Ugly Truckling's identical twin with a load of hurricane wood and boat parts to build various swamp projects. The Pool Guy was "from people" so we bonded right away and he taught me how to throw my new cast net. After the whole pool consultation he departed leaving us with fond wishes and an estimate that called for a team of Mexican specialists and a cost of thousands.

My sister departed to explain to the neighborhood that I wasn't dangerous and I was going to leave soon so their property values could recover. That was my chance to tell Dave about some magic goop that could maybe fix his pool for cheap.
The rottenest leakiest part of a boat is the centerboard trunk if it has one. By the time you get to it it's made of cheese, algae, diesel, and running water. There's a white goop called "3M 5200" that seals centerboard trunks onto boats. Surely it would work on a pool.
Dave was skeptical. Somehow he had the idea that advice from me should be taken with a grain of "not" ahead of it. I turned to a greater authority than myself, "any random stranger with a webpage" and fortunately there was one who'd smeared 5200 on his pool and then never updated his page.

To make a long story short, we tried it, it worked, and it's still working. The trees seen here and the fence and the furniture got smashed to smithereens in the last hurricane. All the backyards were flattened together into a big field of garbage. So they bought new trees and stuff, the pool is still perfect, and I hear the place looks better than before.
I'm welcome to visit again sometime.