Services for adults with suspected ADHD have very long waits both locally and nationally.
Your GP may not be able to enter into “shared care” arrangements with online/remote/other providers for Adult ADHD care, and therefore may not recommend an NHS referral to these providers. Or they may be able to refer to alternative providers “for assessment/diagnosis only”, but not able to share care for treatment. They may recommend that a referral to the local provider is in your best interests, even though the waiting list is long.
Your GP may suggest a referral to the private sector, but would not be expected to enter into “shared care” with private specialists, as the NHS GP. This is a “commissioning gap” where the services available on the NHS do not meet the needs of the population and it has been raised locally and nationally.
You may wish to raise it yourself, e.g. with your MP and/or with the ICB: