Is forgetting birthdays, bills, appointments actually ADHD?

Chronic forgetting of time based responsibilities can absolutely be part of ADHD. Prospective memory, remembering to do something in the future, is often impaired. It is not about not caring. Many people feel deep shame because they do care. The issue is external tracking systems versus internal recall. Calendars, automated reminders, and visible cues are not crutches. They are accommodations for how your brain processes time.