CONVERT Modified dates, December 25th 2020 11:15:23 PM AND 12/25/2020 11:15:23 PM, to 2020-12-26T07:15:23Z AND 2020-12-25 23:15:23-08:00, to UTC

I believe that wneclass2018 wants to tag MKV files with a date in a specified format. Run a TOOL Command, based on selection, in a SINGLE WINDOW

And I agree that %_file_create_datetime_raw% might be better suited for that purpose.
I'll wait and see if he returns with more information.