As I said getting a diagnosis varies by region and doctor. A lot. It's practically impossible in some countries. And also depending on region or personal circumstances, it may not be easy to find another doctor or psychiatrist. Also note that in many countries, only a psychiatrist can diagnose it. Even if diagnosed, you might live in a region where most medicine for ADHD is illegal or have a doctor that won't prescribe them. If you just get disbelief after 6 months of waiting, and after another 6 months just get told stimulants are bad, you might give up.

If you search (eg reddit) for ADHD adult diagnosis, it is filled with horror stories. There's even lots of posts of people diagnosed and medicated for 20+ years that move to another country and can't get a prescription. Or you get a prescription, but the pharmacy won't dispense it or insurance won't pay for it. A typical post on these topics also has one or more people responding "I'm in the same place and it was easy" but also has one or more people responding "I'm in the same place and I tried for 3 years before giving up". By the way, it's also common for women to have more trouble getting a diagnosis compared to male siblings and friends with the same symptoms.