Hit me. If my wife got her way we'd be down around St. Petersburg to Sarasota
Well you’ve already mentioned Siesta Key, which is like white powder sand.
Further south is Nakomis, which has a more traditional sandy beach.
If you head down to Fort Myers, Fort Myers beach is back open. Sanibel Island is opening up too. There is the National Shell Museum and just general renowned shelling. I'll be there myself next Saturday
Continuing down the barrier Island (Estero Island), there are Lovers Key and Delnor-Wiggens state parks.
At about that point you start hitting the Naples beaches. The main Naples beach is quite nice. The pier is still destroyed from Hurricane Ian, but the beach and facilities are fine.
Lastly, there is Marco Island. Lots of good powder sand there. My favorite is Tigertail beach. It's a about a half a mile walk to the main beach, so it keeps the crowds down a bit. Lots of good shelling there as well.