People with ADHD can indeed talk a lot, but this is not always the case. For some, excessive talking is a symptom of their disorder, while for others it is not.
For those with ADHD who do talk a lot, this can be due to difficulty focusing or staying on task. People with ADHD may also talk a lot when they are excited or anxious, as they are trying to express their thoughts and feelings in an effort to make sense of them. When they are talking, they may also be trying to work through a problem or make sense of a situation.
In addition, people with ADHD may also talk a lot because they are seeking attention or validation. This may be because they were not given enough attention or validation as children, so as adults they are seeking it out in different ways.
Overall, not all people with ADHD talk a lot, but for those who do, it can be due to difficulty focusing, anxiety, seeking attention or validation, or just being excited. It is important to remember that these behaviors are often not intentional, and that understanding and patience can go a long way in helping someone with ADHD.