Windows client leaves undeletable data directory after uninstall

An uninstallation of the latest Windows client software left the former sync directory on the client undeletable. The client is a W10 machine.

All files and virtual dummies in that folder and subfolders got a grey cross in Win-explorer, which seems to be known from MS One Drive offline files. Deleting that folder in Win explorer crashes after 2 secs. and is also impossible from the cmd as admin. Already took ownership, adjusted rights,…

Reinstallation of the client software seems not really an option as I don’t want to mess things up on the server.

Any help and suggestions appreciated.