OneDrive - Preview Sync problem

I had issues on some machines where both the classic Onedrive for Business and the next gen sync client were installed previously: the registry key handling the 'grvopen' protocol (that is called by that sync button in the document library), resulting that nothing really happened when I clicked on the sync button.

So if every other attempt would fail, double check the following key in the registry:

HKCU\Software\Classes\grvopen\shell\open\command

Here the proper value should be something like:
"C:\Users\yourusername\AppData\Local\Microsoft\OneDrive\OneDrive.exe /url:"%1"