Are there examples of an API where I can pass a lat, lon, date-range and get NDVI time-series for that location based on Sentinel-2 data without having to download entire tiles and without having to run on GEE? I haven;t seen any complete examples of this e.g. with sentinel-sat API
Are you referring to a point-based time-series?
If so, Sentinel Hub's Statistical API would surely fit:
You will need to configure a layer, which will return actual NDVI values and then use this in the request.
The Python integration is available here:
(Disclaimer: I am working at Sinergise, which is operating Sentinel Hub)