Two ways are possible:
UnitConvert[Quantity[1040, "Seconds"], MixedRadix["Minutes", "Seconds"]]
UnitConvert[Quantity[1040, "Seconds"], MixedUnit[{"Minutes", "Seconds"}]]
Though the first shows up in red (incorrect syntax), but somehow works...
See also the examples that describe how to get mixed units:
Column[Join @@ ("PropertiesRelations" /.
WolframLanguageData[
Entity["WolframLanguageSymbol", "UnitConvert"],
"DocumentationExampleInputs"])]