The Subgrid OnLoad event handler is the correct choice because it executes every time the subgrid is loaded or refreshed. This behavior covers both scenarios specified in the question. The event fires initially when the form containing the subgrid is opened. It also fires again whenever the data within the subgrid is manipulated in a way that requires a refresh, such as sorting the records or navigating to a different page of records. Therefore, a single JavaScript function attached to this event can handle both required conditions.

A. Grid OnSave: This event is specific to editable grids and triggers only when a record within the grid is saved, not on form load or grid sort.
B. Grid OnRecordSelect: This event triggers when a user selects a specific row in a grid. It is not associated with the initial loading of the form or sorting the grid data.
C. Grid OnChange: This event is for editable grids and fires only when a cell's value is modified and loses focus. It does not fire on form load or grid sort.

1. Microsoft Learn | Power Apps | GridControl OnLoad event: "The OnLoad event occurs every time the grid is refreshed. This includes when a user sorts the grid or changes pages." This source directly confirms that the OnLoad event for a subgrid handles both the initial load and subsequent sorting actions.

Section: GridControl OnLoad event

2. Microsoft Learn | Power Apps | Events in forms and grids in model-driven apps: This document provides an overview of the different events available for client-side scripting. It distinguishes between form-level events and grid-level events, clarifying the specific triggers for each.

Section: Grid events

3. Microsoft Learn | Power Apps | OnSave event (Client API reference): "Occurs when a record in an editable grid is saved." This confirms that OnSave is tied to the save action, not loading or sorting.

Section: OnSave event (Client API reference)

4. Microsoft Learn | Power Apps | OnRecordSelect event (Client API reference): "Occurs when a single row (record) is selected in an editable grid." This confirms OnRecordSelect is for row selection only.

Section: OnRecordSelect event (Client API reference)