I have been unfortunate enough to not be diagnosed with ADHD until middle age, and I'm sorry to hear about your apparent misdiagnosis but for people who actually do have the condition, it's very real and it very much sucks. It's not just "someone walked into the room and I lost my train of thought", it's "I have one simple task to do and I know exactly how to do it and it's been hours but I still can't make myself do the thing no matter how much I want to."

It's "I haven't done my taxes for 18 months even though it would only take a day, and I cannot force myself to do it no matter how hard I try."

It's "I've been unable to fold my laundry for six weeks even though I've alphabetized my cutlery drawer, twice."

It's "I have to document this project but no matter how much I want to just do it, I nevertheless continually find myself on imgur or Facebook or Hacker News or some random other website reading up about how switched-reluctance motors or Monte Carlo tree search or whatever works."

It's lack of executive function when you need it and it's the inability to think about anything else when something's grabbed your focus and it's a built-in character flaw that you can't "just choose to not have" and it's growing up thinking you're "just lazy" but "have so much potential" and it just. f*king. sucks.

If all you need in order to focus on the thing you want to focus on is for no-one to interrupt you, you don't have ADHD.

/rant