As far as I can tell, they say: "Mission control and data distribution are managed by EUMETSAT." They have published their own blog post here: https://www.eumetsat.int/features/see-earths-atmosphere-neve...
There they say that: "Observations made by MTG-S1 will feed into data products that support national weather services …". So I guess there will be no simple, publicly available REST API or so... but if anybody finds anything, let us know here :)
For the datasets, I tried to access (like the full disc image in visible wavelength, MTG 0 degree), it is sufficient to register at eumetsat to get a username and password. The eumdac python tool is probably the easiest way to access the data:
https://pypi.org/project/eumdac/
(If you do not want to use python, the --debug option is quite useful to see exactly the request made. The output is either some JSON metadata or a large zip with the netcdf data)
Most weather data isn't generally available by easy to query REST API's (at least not at the original sources). One side project I had I wanted to use NOMADs data, and it was quite a grind downloading and processing the raw datasets into something usable at an application level (or viable to expose via an API).
That’s why you have service/products that have the sole purpose of taking all these region specific data sources and processing them in to a generic json api.
The government orgs probably do it intentionally so they don’t have ten million devices pinging their servers to update weather widgets.
Check out open-meteo. They’ve got pretty extensive historical and forecast weather apis in easy to consume formats. https://open-meteo.com/en/features#available_apis
https://user.eumetsat.int/api-definitions/data-store-downloa...