I'm working on a modern Word Add-In that we would like to work inside Word for the Web on Office Online Server (2019) via WOPI. For testing, we would like to sideload the Add-In. I can do this in the O365 version of Word for the Web without problems, but the only option on OOS appears to be loading Add-Ins from AppSource. I also understand from various (informal) posts that centralized deployment is not available in OOS. Does anyone know if it is possible to enable sideloading in OOS?
By sideloading, I mean manually uploading the manifest.xml file via the "Add-Ins" button on the ribbon bar. In O365 this option is called "Upload My Add-In".