Metadata table for relationship:

This method can only set existing data to read only, but could NOT prevent user from creating new data in WebUI.

This method can allow you ( GenIL layer ) to add some post processing of data retrieved from API layer

It works as screenshot below.

How to disable these two buttons:

Approach 1: change enabled attribute in gt_button

Appraoch 2: hard code displayMode = read only

How to disable Edit List button:

Same idea: