I created a collection named "Pictures" and I added two fields; The first field titled as "desc" and the second one was a "realtion field" which links it to another table. After creating a record, the "linking field" was not exists on response API.
you need to pass ?populate=item
in your api it will showing in result. any relational data or any media default not display. in strapi v4 you need to pass a populate as a query params for viewing the data