Jetpack vs WP-Rest Api

Hi there,
i use the jetpack-public-api to get Response from my own Webservice to fill my App for local Tourism.

Most of all entry have a Query like this:

https://public-api.wordpress.com/rest/v1.1/sites/122035992/posts/?fields=URL,post_thumbnail,date,title,featured_image,excerpt,content

Much more i didn’t need at this time and it works very well.

Now i make my First Steps with the WP-Api and i’am not able to query the fields i need.

https://appviewer.mzs-stade.de/wp-json/wp/v2/posts/

this gave me to much information i didn’t need. And i’am not able to get the featured_image. Is it really much more complicated as the jetpack-public-api?
It would help me for understanding if some could ?translate” my Query to the new Version. The documentation is not very helpful for me, i read it several times.

Please note, I’am not a developer, just a graphic designer who must Do the Job.