My first recommendation would be to talk to your doctor and see if you can get tested by a specialist. It can be really difficult to diagnose, especially with comorbid disorders like anxiety.
I’d also suggest making a list of symptoms you exhibit that could be adhd, and another list of things that you feel might point away from it. It might also help to examine the way you think and interact with others. Are you impulsive? Do you tend to have many racing thoughts? Any experiences with executive dysfunction, fidgeting, etc? It sounds like you can hyperfocus but also tend to get distracted when overwhelmed by information.
Also, examples of notably not showing adhd symptoms can always be examined more. Is being early a coping mechanism to prevent lateness? Could your success in school be attributed to being interested in the material, or a successful set of habits to prevent yourself from being overwhelmed? You seem to have trouble with multi-step directions when they are spoken, such as directions, but are fine when they’re written down or presented in certain ways, like in your example about IKEA instructions. You also mentioned carrying paper everywhere. It’s possible that your situation is similar to that of my mother, who has mild ADHD but successfully managed her symptoms through various self taught coping mechanisms. Are there other odd habits you’ve formed to help yourself function that others don’t necessarily need? Are there strange behaviors you exhibit that aren’t necessarily symptoms, but could be related to them?
Another thing I’d recommend is talking to family, friends, etc. about what kind of symptoms you may exhibit or what kinds of symptoms you may have had in the past. It’s hard to remember how you responded to things in the past, and it can also be hard to gauge your own symptoms. If you do have ADHD, it’s also totally possible that you aren’t great with self awareness and thus there may be some things you haven’t picked up on.
That’s my 2 cents. I’m no expert by any means, but those are the things that spring to mind when I read about your situation.