Its a lot more complex than just a fan door - and all computer controlled and sequenced to ease pilot workload in comparison to the Harrier.
If you check the history of the development programme the door and mechanism is an area which was substantially redesigned and strengthened, first changing from side opening bi-fold doors to the single rear-hinged flap, then strengthening the bulkhead =, hinges and flap as well.
https://aviation.stackexchange.com/q...ing-transition