Project Is Unviewable

It was possible to create an Excel add-in that did not appear in the VIsual Basic Editor but this functionality seems to have stopped working.
These were the steps but they no longer work in Excel 2019.

Save your Workbook as (.xlam)

Save the Excel (.xlsm) workbook as an Excel Add-in (.xlam).
Select File, Save As and change the file extension to (.xlam).
Change the folder location at the top to be the same folder as your Excel workbook was (not the default add-ins folder).
Press Save and close the (.xlsm) workbook.

Lock the VBAProject

Press Alt+F11 to open the Visual Basic Editor.
Find and select the corresponding VBAProject in the Project Explorer window.
Right mouse click and choose VBAProject Properties to add a password.

Change the isAddin property

Double click on the add-in (.xlam) file that you just created. This will load the add-in into Excel.
Press OK to close the VBAProject Properties dialog box.
Select the "ThisWorkbook" code module.
Press F4 to open the Properties window.
Change the "IsAddin" status to False.
Return to Excel to see your workbook displayed.

Share the Workbook

Select File, Options and select Quick Access Toolbar.
Change the "Choose commands from" drop-down to "All Commands".
Find the command "Share Workbook (Legacy)".
This will add the command to your Quick Access Toolbar.
Press this command.
Tick the "Use the old shared workbooks feature instead of the new co-authoring experience".
Press OK to close the dialog.
When prompted to save, Press OK.
You should see a prompt saying "This workbook contains macros recorded or written in Visual Basic. Macros cannot be viewed or edited in a shared workbook.
Press OK.
Check that the word "Shared" appears in the Excel title bar at the top.
Open the Visual Basic Editor and try and open the VBProject.
You should see a message saying "Project is Unviewable".

Resave the Workbook as an Add-in - Not Working

Save the Excel (.xlsm) workbook as an Excel Add-in (.xlam).
Close this Excel workbook without saving the changes.
Test out your newly saved add-in (open it, access the vbe, try to expand the project window, you should get the new message "Project is Unviewable"