I would like to have it in a separate column showing the difference in minutes. Thank you!
Multiply the difference by 1440 (* 24 * 60)
Because the unit of the datetime values is “Days” in the spreadsheet applications. Format the resunt az a decimal fraction number.
Or format the difference by a Cell Style containing the format code [MM]:SS.
In this case the result still in Days unit, but the result will be formatted as minutes.
… and since the question is “showing the difference in minutes”, the latter option (using [MM] with or without seconds - as desired) is IMO better.