Middle aged, diagnosed with ADHD about 15 years ago, been in the industry for 25 years.
Not saying my way is best, but this is how I do it.
ADHD is nothing to be ashamed of, and IMO you have as much right to accommodations as somebody with no legs who uses a wheelchair. However, you couldn't pay me to mention ADHD to an employer or prospective employer. It's too stigmatized, and also it's just plain nebulous -- even if an employer is supportive, your manager can't intuit and extrapolate the behavioral health needs of individual employees based on their diagnoses.
How do I best tell prospective employers I might need
some accommodation in this process?
During the interview process I don't mention ADHD or accommodations at all. Best advice I can give here is to either (a) just grind Leetcode until you feel comfortable with it? (b) send your resume to a kazillion places and just bail if the interview process involves some kind of live coding exercise you feel that you'll struggle with. Or, alternately, just do it anyway with zero pressure and maybe you'll surprise yourself. You
will get better at live coding and interviews with time.
Once you have the job, I still never mention ADHD ever. What I do is just ask for accommodations that I need. I never worked at a company that really gave a flying fuck if I took my laptop to a spare conference room so I could code in a quieter and less distracting environment. Helps to tell your team where you'll be so it's not like you disappeared.
But from a tactical standpoint I would at all times urge people to think in terms of solutions (specific coping strategies and accommodations) instead of labels and craft your employee/employer relationship accordingly.