I think what they meant was that they participate in only 10% of conversations because when they do they talk too much. Nothing about OP’s post tells me they’re not aware of the problem or in denial of it. Their question was how to stop doing it.
I think you’re taking it for granted that if someone knew about the problem and tried hard enough, they’d be able to stop, so you’ve answered assuming that they mustn’t be taking it seriously else they would’ve quit doing it already- only there’s a lot of reasons why it might be extremely difficult.
ADHD is one of many reasons, and it’s not a matter of willpower. This is why it requires medical and psychological intervention to treat effectively, and it is by far not the only cause of overbearing social behaviours.
I replied with this to another user already by I think this applies here, too: I think what they meant was that they participate in only 10% of conversations because when they do they talk too much. Nothing about OP’s post tells me they’re not aware of the problem or in denial.