Why does Mail App for Office appear in Outlook online but not in my installed Outlook Client?

I have developed an office mail application.

It shows up in my Office 365 Outlook in my browser, but not in my installed client.

But in my installed client it looks like this. Those. the application is not displayed:

I have looked at app management etc but can't find any options to get it to show my installed client.

Any ideas?

Here is my manifest:

Note that this is not a real application, but rather a "try things out" application.

OK, so here's my version of Office:

And here is my updated manifest file as requested by @andrews I am removing regex rules to make troubleshooting easier:

I haven't installed the app, restarted everything and I still can't see it in my desktop for Outlook.

thanks Russ