For example, currently you can run the add-ins in Word Online (hosted on Office 365) but running Word Online hosted on Office Online Server the add-in functionality is not available.
We are going to write apps for Office 365 (Word online, Excel online en PowerPoint online) and have installed Office Online Server with SharePoint 2016 in our isolated test environment. Unfortunately, I don't see the Store button on the ribbon where I can upload my manifest file of my app.
Is this totally unavailable in an Office Online Server or do I have to enable something somewhere?
Dmytro Lapshyn commented
I believe this is really essential for enterprises, as it is an enabler for quick Office-based solutions for internal needs, that would otherwise require developing a full-fledged Web application.