Find a live webcam to follow and you can see the conditions. The sargassum should be clearing up from this point .Edited: 26 September 2021, 05:23
I don't know if you are aware of this, but sargassum is typically present from about late February/early March until about September/October (and that depends on how much is in the sea) with the April to June being the worst period. There's typically little to none from November until the following February.
After June, it begins to abate, and I began noticing an improvement at Playa del Carmen in August (some days with no sargassum, some days with small amounts). In 2020, it was gone by August.
I was hoping someone would reply specifically about Cancun beaches, but since no one has yet, here's a media report about the improving situation...