Memorable beaches in Italy are plenty but few Americans have ever visited those localities, including many in this forum, because they are not near the typical destinations Americans go to.
The Ligurian coast (Cinque Terre), a popular destination also for Americans, has jaw dropping coastal views, but it is a very mountainous region, with mountains dropping into the sea, therefore what you have is a lot of cliffs, with small pebbly coves and beaches, but not really sandy beaches.
The exact same is true for the Amalfi Coast, Capri, and much of the Campania coast (Naples area). That coast is super beautiful, but very cliffy, so at most you get some nice small pebbly beach, but no white sand beaches.
If you are looking for memorable beaches, with great sandy beaches, you would need to venture off the American tourist beaten path.
Sardinia has some of the best in the world, not just the Med:
Sicily has a few also. The most famous beach is at San Vito Lo Capo, western Sicily.
But Americans who visit Sicily, generally prefer to visit the cities and the Greek ruins, not the nice beaches that aren’t so easy to reach.
Puglia has beautiful beaches too, in particular on the Salento Coast or the Gargano Peninsula (which however is kind of cliffy too)
The smaller Italian islands (Tuscan Archipelago, Ponziane islands, Gulf of Naples islands, Eolie islands, Egadi islands, Tremiti islands) have great places too, but they are not easy to reach, and many are cliffy.
You will not find memorable beaches near Venice or near Rome, or near Florence in Northern Tuscany (Versilia), but those are the ones most Americans have seen since they are easy to drop by from the aforementioned top destination cities.