The answer from 5-10 years ago was a recommendation to implement this API
and also follow those protocols. I believe some vendors may have done this, the NHS D managers didn’t document what was done. This is not the same as the GP Connect API, which is bespoke.
Around that, I (and I stress I) would suggest they follow EU recommendations https://euridice.org/eu-health-data-api/
That is the closest to NHS England previous viewpoint ….. and also stick to HL7 UK Core profiles (which basically means base FHIR)