add a comment but thought that here was better. Problem with accessing ribbon

Much of the functionality for each controls in each of the tabs of the ribbon are only available/enabled when it possible to do actually do something. If a workbook is read-only, there isn't much you can do (you can't edit or manipulate the data), so most of the controls in the ribbons will be disabled until such time as you click somewhere (like an editable cell). The same applies when you have a protected sheet or workbook.

As an aside, why do you need to open the addin in read only mode? By default (and by design), addins are not visible in Excel, and if there is meant to be user interaction with the addin, this is ordinarily through context menus/menus, the ribbon, the commandbar, etc. Sometimes an addin might have worksheets on which it will store data, etc or use as a form of user input, but in those cases, I think that the standard approach is to make a copy of the worksheet into a new or existing workbook, and then process the user input from that sheet rather than change the data on (what are ordinarily) hidden worksheets. Even then, if there is concern about the user editing the contents of (even) hidden worksheets, then the usual approach would be to protect the worksheet rather than loading the addin in read-only mode.

Not really following the problem, can you post the addin so we can try it?