So the Office 365 ProPlus Click to run has been upgraded to match the Office 2016 version. But unfortunately it has come with a small bug when accessing the preview for Excel.
I’m sure this will be updated soon and when running click to run enabled updates and I hope You all do it will be fixed. But in the meantime You can apply this quick fix.
The error shows up like this when trying to preview Excel spreadsheets:
There You can see that the Excel previewer has a slightly different value.
Delete the REG_EXPAND_SZ key and create a new String value (REG_SZ)
Value: Microsoft Excel Previewer
Restart Outlook and Excel preview will work!