Power BI custom connector

Hi VedantChauhan,
Thanks for reaching out to the Microsoft Fabric Community forum.

For the filter selection requirement, Power Query custom connectors support function parameters with predefined values. Using Documentation.AllowedValues changes the parameter input from a text box to a drop-down list. The selected value can then be handled by the connector logic when constructing the API request.

For table/entity selection, the documented approach is a Navigation Table. Power Query displays the Navigator after the required parameters and authentication. Navigation Tables can also be nested/multi-level, allowing hierarchical selection of entities.

For the navigation flow, the documented approach is to use Navigation Tables, including nested Navigation Tables for multi-level selection.

A suitable flow would therefore be:
Parameters → Authentication → Navigation Table → Entity/Table selection → Data retrieval

For more information, please refer to the below official Microsoft documentation:
Add Function Documentation - Power Query | Microsoft Learn
Handling navigation for Power Query connectors - Power Query | Microsoft Learn
Handling navigation for Power Query connectors - Power Query | Microsoft Learn

I hope this helps. Please feel free to reach out if you have any further questions.
Thank you.