The floating floor at the skeleton piano

Its a plot hole

I have no idea but it’s entertainment so just accept it lol.

I didn't think that it was an abyss, just a deep hole. They don't show what is underneath, so it's very possible that the bone organ was held up by stone pedestal. I honestly never thought that it was floating until you mentioned it.

It wasn't floating.

It was attached to the wall behind the organ itself.

Presumably, a final mistake would drop the organ into the abyss, leaving nothing to stand on (though there was apparently a ledge around the whole room that the Fratellis used).

Also, you can see what's underneath in some shots; it's a deep pit lit by blue fog with stalagmites sticking up all over.

I had the same thought on the 2nd challenge that indiana goes through in "The Last Crusade". How does stepping on the right letters keep him up but only the wrong letters crumble with a giant abyss below?

It's a cartoonish fantasy-action movie for kids, not a documentary about structural engineering.

Is it possible you didnt analyse the construction of the pirate organ disappearing floor trap sufficiently and each section of the floor was indeed independently attached to the organ in case of this exact situation?