Where are the turtles! I've looked for nearly half an hour on the beach and nothing spawned. I move around a lot. If that's the problem please tell me.
If you wait on one beach for turtles to spawn, you may wait for a long, long time yet. Turtles, being classified as peaceful mobs, are under the same mobcap as other peaceful animals, and that mobcap is practically always full.
Get in a boat and start traveling along shores of oceans, until you find some turtles - it usually doesn't take very long. Then you can breed two of them with seagrass, gather the eggs using a silk touch tool, and place them on sand somewhere near your base. Make sure the area is well lit up and protected from hostile mobs as zombies, drowned and zombified piglins (spawning from Nether portals!) will actively seek out the eggs to destroy them. During pre-dawn hours in player vicinity the eggs will start hatching, and baby turtles will spawn - and they'll consider the sand they spawned on their "home beach" and keep coming back to it if allowed to roam freely.