Personally I think the future of desktop applications should be designed around the premise of localhost first and cloud second. The ability of the locally host application to synchronize to the cloud or central repository (similar to rsync and Git) should be the default not the other way around (I am looking at you Microsoft Teams). Technically there should be no different between people working independently with their local copy of data to be merged centrally later, and an offline application with an intermittent internet connection.
Now with readily available VPN tools like Wireguard becoming more popular the notion of using web applications for distributed authoring and collaboration, etc, is not necessary anymore. But if you insist to use web based technology there is always protocol like webdav to the rescue. If you do not want either of them (VPN and webdav), the recently announced SMB over QUIC can be a very good alternative solution [1].
[1]https://redmondmag.com/articles/2020/03/02/microsoft-smb-ove...