Earlier quoted context omitted.
FAs can be really strange about that kind of stuff, not just out of ignorance. My kid liked to suction cup his GoPro to the window to take a time lapse movie of the flight and one FA told him he had to take it off the window because he was, and I quote: "modifying the structure of the aircraft and that's not FAA-approved".
There has been a lot of debate in the aviation maintenance community regarding the legality of attaching gopros etc. to aircraft with suction cups. Someone eventually wrote to the FAA chief counsel and asked. "Another consideration, in the case of this type of equipment, is the applicability of the term "alteration". FAA Order 8110.3 7E, defines an alteration as "a modification of an aircraft from one sound state to…
That memo is about attaching it externally. Attaching it to an internal window is probably a non-issue.
I once had a security agent ask me to prove a GoPro was a camera because they didn't understand how there could be no screen or viewfinder. It was most frustrating because this was an area where they would have encountered it many times (lots of scuba divers).