I've read many naruto fanfictions and none of them have gotten hand seals right, first hand seals were literally made to guide chakra by molding said energy in a preordaned way to achieve the casting of a jutsu.
I've seen many writer put that transmigraters could not simply used jutsu they remembered from their previous life because of some sort of need to know the flow of chakra that is wrong.
The flow of chakra for a jutsu comes in when you as a shinobi are either trying to lessen or get rid of hand seals all together.
Hand seals are they key to learning and using techniques.