Continuing issues uploading Word add-in project manifest to AppSource

I'm going to create another question here because this is the only way I've been able to get meaningful responses from the Microsoft Office support team. Please see this question for the last question on this subject I asked, the response, and my questions in response to the response (which have yet to be answered.)

I'm trying to upload an existing Word add-in project to App Source. There is currently a submission for an app which we've created, existing here:

When I click 'continue submission' I see the following:

When I click into 'Packages' I see the following:

At no point am I prompted to, or able to, upload a manifest.xml file, which I've been told should be a step in this process.

Is this somehow the wrong submission type which we've begun? If so, what should we have done to get to the point where I can upload my manifest file to begin the add-in validation process?

Please be as explicit as possible when describing any steps I should take, so that I can be certain if the options I'm seeing aren't the ones being suggested. This has been an incredibly frustrating few days trying to begin the process of validation for my add-in.

Thank you.

Edit:

This is the screen I'm brought to after I click 'Office' when I first go to the SellerDashboard.

Nowhere is there an option to create a new Add-in. If I click 'Windows' and 'Products', it brings me to the existing add-in whose submission I'm unable to add my manifest.xml file to.

It seems like you are trying to upload in the wrong location. To submit Office Add-ins to AppSource you need to upload via the SellerDashboard and select the Office program in order to submit a Word add-in.

Once you select Office, click on 'Add a new app' and select 'Office Add-in'. Then you will see the prompt to upload your .xml manifest

If you don't see Office, as your latest comment states, please ensure you are registered for the Office program.