To retrieve the last member of a set you can use the TAIL() function.

The following example returns the total turnover over the last member in 2020-02 for company 4711.

SELECT {
	TAIL(NONEMPTY([DatumStapel].[JMT].[T].Members, { ([Datenherkunft].[Datenherkunft].&[200], [Company].[Company].&[4711], [DatumStapel].[JMT].[M].&[2020]&[2]) }))
} on columns
, { [Measures].[Umsatz] } on rows
FROM [Finance]