Very few things are known. What we do know is that at one point contact was lost with the booster and later it was declared a complete loss.
I'm not saying it's impossible that it did an autonomous soft landing in the ocean, but that would surely be mentioned and hopefully even shown.
Leaving us with the logical conclusion that it had an uncontrolled descent with a hard crash. Whether it fell as one piece of debris or a shower of fragments is of course unknown. A complete loss of telemetry points towards an energetic failure. But it is possible it was a simple comms failure. So maybe I shouldn't have compared it to the starship fireworks, it might have been intact until it hit the water.
Had to do a hard reset today. Quite annoying, but most things synced back automatically.