All data lost means all connections lost, i.e. folders and devices. The directory contents themselves were all still there.
The installation was set to default after the update. All folderinformation and devices were gone and had to be reconnected. In this case it was not a bad thing, the external devices were immediately offered again and the directories were quickly reconnected.
It was a Windows 10 computer with only a few connections. If this had happened on one of my servers, the effort would be more much extensive.
Can I make a backup of the working folder
C:\Users\xxx…xxx\AppData\Local\syncthing
as backup to restore it in such cases? Or is to store the “config.xml” enough?
If possible, I make a second test on a other windows computer as test.