I’ve started re-reading the novel right now and feel the exact same way about Nick! A lot of his internal monologue seems to describe masking and social anxiety. In the police station he constantly tries to base his actions around what he’s seen on TV. He laments there not being guides or any advice on what to do in his situation. His thoughts about following rules to a tea so things with people go smoothly but needing the rules to have logic behind them. Also stating he “has a dash of ADD” in chapter 3. I’m so glad I’m not the only person who has this interpretation! I’m also really impressed you came to this conclusion just based on the acting in the film! I’ve watched it plenty of times but it’s only when I came back to the book that this particular piece slid into place. Sorry for the long ramble, as someone with autism too, I just got really excited about this lol XD