@boka003 creating an API to allow showing posts with specific field values is beyond the scope of help the you’re probably going to find on this forum.
The limit of my knowledge is that you’re going to need to create a custom end point for the WP REST API. When this custom end point is called a query needs to be done to get and return the posts that you want to be shown.
https://developer.wordpress.org/rest-api/extending-the-rest-api/adding-custom-endpoints/
https://www.google.com/search?client=firefox-b-1-d&q=wp+json+api+create+custom+end+point
