I have same problem too!
i use iphone X with storage 256GB, wanted to move to iphone 12 pro 256GB, i didnt used all my 256GB but it keep showing failed to transfer as not enough space.
what do you mean not enough space where my iphone X have plenty of storage?
and whats wrong with HEALTH app? It took 15.58 PB? Tried to clear every data and it seems not doing anything.