Is it normal/OK for LED lights to “crackle” when turned off?
I am not sure this is the correct answer but why let that stop me from postulating?
I have heard this in some light fixtures and my educated? guess is it is the sound of contraction ( as in expansion and contraction due to heating and cooling )
Some of the parts of the fixture expand from the heat produced by the light, when you turn off the light the fixture starts to cool and contract, I.E. return to its shape/size when not hot.

Is it normal/OK for LED lights to “crackle” when turned off?

Normal, ?? -  ok, YES.