I have issue I cant seem to solve at the moment: all search results (and this includes items returned in the "Highlighted Content" web part) don't seem to want to open with the client application. So, if a bunch of docx files are returned in a search, clicking on a file will result in downloading a copy / showing the save prompt. Libraries are all sorted for opening in the client application, if I open a file directly from a library it opens up to edit in the client app.
I have tried a few things such as returning to the classic experience and editing the search preferences to open in client application (which doesn't change anything in classic or modern experience). I have also changed the settings in Central Admin of the Browser File Handling to Permissive - no impact. The feature to open in Client App is active and all libraries are set to open in client app.