You aren’t supposed to wander off or daydream when watching something.

Again, people with ADHD aren’t constantly daydreaming.

You are supposed to take in the characters, dialogue, cinematography, animation, etc., take in the story, and follow it. Escape into that world, not focus on anything else. That’s how you watch something.

You keep emphasising on how you are “supposed” to watch a film, again you are speaking as if people with ADHD aren’t doing what they are “supposed” to do.