All is working now. Must be an update from win10
my working rev is
2018-12 Cumulative Update for Windows 10 Version 1803 for x64-based Systems (KB4471324)
win10 startmenu/settings/apps/default apps/chose defalut apps for file types.
*.grf isn't listed.
see also https://www.digitaltrends.com/computing/how-to-change-file-associations/
and the nuget
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