LogicApp custom connector dynamic schema response fields

Thank you @David Meu, For confirmation. Posting it as an answer to help other community members.

Question is why am I seeing also Body and Item fields while they are not appearing in my schema response:

AFAIK, Body and Item are inbuilt objects for any result from previous steps, that are listed under dynamic content. When the previous result has more than one object in its entity, it provides a variable as item which refers to each entity from result so you can easily refer in looping activities to iterate. and Body is just whole reference to the result or response from the earlier step, it is json of complete result as it is.

Because they are not appearing in other connectors responses (Outlook 365 for example)

We can see the body field (e.g) in Outlook 365 .For activities which have results will only produce that option .so its depends on the activity .

For more information please refer this Microsoft Documentation: Call an API from a Logic Apps workflow using a custom connector & Extend an OpenAPI definition for a custom connector