This should be fixed in WinSCP 6.0.2 RC:
Issue 2175 – The first copy&paste or drag&drop of remote files to other application might fail in Explorer interface

In principle, the solution for the help:
https://winscp.net/eng/docs/ui_pref_dragdrop#fake_file

It worked, and fixed the error when I added the line C:\
But in the WinSCP-5.19.6-Portable version there is no such error and nothing needs to be added. Is it possible to fix this error in future versions?

Updated from WinSCP-5.19.6-Portable to the latest version of WinSCP-5.21.8-Portable at the time of publication. And the problems started, I switched the interface to <Explorer >, re-entered and went problems with drag &drop when trying to throw over the aisles of the application gives an error! Error: WinSCP could not detect the folder where the files were dragged. If you click OK and move it again, then there is no error and the file has moved. In fact, this error occurs every time you start. But if the interface is returned to <Commander>, then there is no such error when dragging to the desktop, outside the application! In the old version, there is no such error. Tell me if it can be fixed?