Something about flashing what is write one good coder with a lot experience:
In ISTA is all module green and no problem with a car should I do software update
Than don’t try to imagine problem
Updating whole car is an adventure - if you are up for it it can be fun, or you may never get to the final destination. F20 /36 are frm based and rather safe to update. Bdc and ZGW based cars not so much