A couple weeks ago a user reported that they could no longer open document libraries in Windows Explorer, when using IE as a browser. I verified I could also not do this. After restarting machines - including the sharepoint server - the problem persists. When the "Open with Explorer" link is clicked for a library a popup appears telling me "We're having trouble opening this library in File Explorer" with learn more link and a recommendation to sync with onedrive. Syncing doesn't fail but I think we did not do the right setup to make that work in our environment, so it doesn't actually result in seeing the files in the library. The learn more link suggests something about adding the site to trusted sites, and says some things about IE10. There's also the webclient service, which was already installed or running on client machines. Had IT add it to the sharepoint server as well.
Users can work around this issue by using a shortcut to the folder in windows explorer via a UNC path.
The environment is SharePoint Server 2016 on-premises and windows 10 clients using IE 11. The task in question has been working until approximately 12/20/19 or thereabouts. No updates have been made to the SharePoint installation recently, and server updates were rolled back with no appreciable change in outcome.
Is this something Microsoft has done? Or is there perhaps something I missed when I tried to correct the issue?