You don't have to have ADHD to hate open offices and find that setup distracting, but it's certainly a possible factor. I know this is boring / dissatisfying advice but going to a doctor could probably add more context to your self-assessment.
We should start pushing to get private workspaces by seeing ADHD as a disability
I think ADHD is actually considered a disability. However, most people probably wouldn't be comfortable telling their boss that they have ADHD. If your ADHD having a negative impact on your performance and you're about to get fired revealing your disability might save you from losing your job. However, I don't imagine being known as the ADHD guy is going to brighten your prospects for future promotions.