disable subgrid – Microsoft Dynamics CRM Forum Community Forum

You can disable an editable subgrid control by first grabbing the grid control (also referred to as the grid context) which is similar to grabbing any other control.  Then disable the grid context.  It’s even in Microsoft’s Client API online documentation:

https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/clientapi/reference/grids/gridcontrol

setDisabled() is listed as an available call for the grid control.

let disableGrid = function (formContext) {

       let gridContext = formContext.getControl(“GridsName”);

       gridContext.setDisabled(true);

   };

However, you can still drill into listed records.  You cannot stop that.