Automatically open a task pane and install add-in

Question

Hello Microsoft team,

Currently I am working on getting office add-in from store to auto open on first launch in Excel file.

I have set the WebExtensionTaskpane Visibility to True and Office.AutoShowTaskpaneWithDocument to True as well in OpenXML.

The current behavior I am getting on Excel Desktop:

1. When user opens the Excel file, the side pane will prompt user to trust the add-in.
2. When user clicks on "Trust this add-in", it will run the add-in.
3. When user saves and closes the Excel file and then reopens it, it will prompt user to do the same thing again.

The current behavior I am getting on Excel Online:

1. When user opens the Excel file, the side pane will prompt user to trust the add-in.
2. When user clicks on "Trust this add-in", it will run the add-in.
3. When user closes the Excel file and it auto saved, it won't auto open the task pane, but the "Office Add-ins" tab showing the add-in is installed, and it will auto load again on next reopening.

What I am expecting is different on step 3, which is,
When user reopens the Excel file, the add-in will auto open without having user to click on "Trust this add-in" again.

Please shed some lights in the expected behavior for Excel add-in to automatically opening a task pane.
Thanks in advance for your assistance.

Reference:
https://learn.microsoft.com/en-us/office/dev/add-ins/develop/automatically-open-a-task-pane-with-a-document
https://github.com/OfficeDev/Office-OOXML-EmbedAddin

Regards,
Yong