[eivarv]

    Could someone tell me how that inspection works? Are there researchers who are given the source code?

It doesn't (with the exception of an exclusive program[0]). Not only do they generally make security work on their devices difficult – they have a history of suing companies that facilitate it [1].

[0]: https://developer.apple.com/programs/security-research-devic...

[1]: https://www.theverge.com/2021/8/11/22620014/apple-corellium-...