Per dozens of engineers at SpaceX...the biography from Isaacson contains numerous exaggerations and outright fabrications.
Elon Musk's involvement in design decisions was limited to the typical executive level involvement in hardware design, in the sense that he was presented multiple options by the engineers and designers and got to pick which one they went with.
Indeed, with SpaceX it's usually immediately obvious when Musk was involved: does something fail spectacularly in a way it wasn't supposed to? That was Musk, getting involved in something he didn't understand and overriding the engineers and other professionals. (Contrast the first Starship launch this year, which Musk micromanaged, vs the second launch in November in which he had minimal involvement due to being distracted by X and Tesla.)