I have an MS. Office Excel add-in and I use it via sideloading of the manifest.xml file.
it works and everything is good, until recently I've noticed that there are some issues when users try to sideload the add-in to Excel for the Web (X-Frame-Options issues that will take some time to fix)
My question:
Is there a way to disable the add-in on the web version of Excel from the manifest.xml?
There is no systematic way of blocking some platforms in the manifest. The best you can do is have code at add-in start up that reads the Office.context.platform property and branches accordingly. If the value is OfficeOnline, then the add-in UI displays a message to the user saying that the add-in won't work in Office on the web and they should switch to desktop Office.