Well, they might be really impressed with how Spider - Man has developed in this fanfiction. Maybe they'll cheer for his new moves or be shocked at the new villains he faces.
Tony would probably focus on the tech aspects. He might think Spider - Man's web - shooters could be upgraded in a certain way. Steve would look at the hero's values, seeing if he's staying true to what a hero should be.
Spider - Man would be very confused. He would feel betrayed because he thought the Avengers were heroes he could trust. He could start by asking them why they are doing this. If they don't give him a satisfactory answer, he might try to escape in a sneaky way, using his spider - like abilities to find a weakness in their capture setup while still trying to reason with them.
Spider - Man would probably be defensive at first. He's used to working alone most of the time, and being interrogated by the Avengers would seem unfair to him. He might crack some jokes to ease the tension, but also firmly state that he's a hero too.
One reason could be a misunderstanding. Maybe some events were misinterpreted, and the Avengers thought Spider - Man was involved in something bad. For example, if there were some crimes that seemed to have Spider - Man's fingerprints all over them, but in reality, he was being framed.
Spider-Man has definitely been in the Avengers in the comics. His presence has added a fresh dynamic and his powers and wit have been valuable assets to the group.
One possible reason could be a misunderstanding. Maybe some villains have framed Spider - Man in a way that makes the Avengers believe he's a threat. For example, Mysterio could have created false evidence to make it seem like Spider - Man is involved in some evil plot against the world.
Well, if the Avengers are watching 'Spider - Man: No Way Home' fanfiction, they might be looking for inspiration. Maybe they want to learn from the different scenarios presented in the fanfiction to better prepare for future threats in their own world. They could also be amused by the wild ideas and crossovers that often appear in fanfiction.
Well, it could also happen that Peter's Spider - Man suit technology gives him away. Maybe the Avengers have some advanced tech - sensing equipment, and when Peter is around in his suit, it gives off some unique signals that the Avengers pick up on. So, they start to look into it and eventually figure out that Peter is Spider - Man.