Rule to Pick Scenario based on comparison between POV time and Time set for column in cubeview

This won't work with this way with a xfbr function, if you are using dynamic time lists like T#2021.base.

Instead, you can create an ud8 function:

Dim currTime As String = BRApi.Utilities.GetApplicationProperties(si).GlobalTime
Dim timeId As Integer = BRApi.Finance.Members.GetMemberId(si, DimTypeId.Time, currTime)
Dim timeId2 As Integer = api.Pov.Time.MemberId

Dim newDataCellPk As DataCellPk = api.Pov.GetDataCellPk()
newDataCellPk.UD8Id = DimConstants.None

If timeId >= TimeId2
	newDataCellPk.ScenarioId = api.Members.GetMemberId(dimtypeid.Scenario, "Actual")
Else
	newDataCellPk.ScenarioId = api.Members.GetMemberId(dimtypeid.Scenario, "Budget")
End If

Return api.Data.GetDataCell(newDataCellPk)

If you want not only the data to change, but the column header as well, you can do it with a xfbr function creating a comma separated list of povs:

Public Function PastBudgetCurrFutActual(ByVal si As SessionInfo, ByVal globals As BRGlobals, ByVal api As Object, ByVal args As DashboardStringFunctionArgs) As String
Try
Dim curTime = args.NameValuePairs.XFGetValue("CurTime")
Dim curTimeMember As Member = BRApi.Finance.Members.GetMember(si, DimTypeId.Time, curTime)
Dim colTimeQuery = args.NameValuePairs.XFGetValue("ColTimeQuery")
Dim colTimeMemberList As list (Of MemberInfo) = BRApi.Finance.Members.GetMembersUsingFilter(si, brapi.Finance.Dim.GetDimPk(si, "Time"), colTimeQuery,False)

Dim povs As New List(Of String)

For Each colTimeMember As MemberInfo In colTimeMemberList
	If curTimeMember.MemberId >= colTimeMember.Member.MemberId
		povs.Add($"S#Actual:T#{colTimeMember.member.Name}")
	Else
		povs.Add($"S#Budget:T#{colTimeMember.member.Name}")
	End If
Next

Return String.Join(",", povs)

Catch ex As Exception
Throw ErrorHandler.LogWrite(si, New XFException(si, ex))
End Try
End Function

You call it this way: xfbr(<business rule name>, PastBudgetCurrFutActual, CurTime=2021M10, ColTimeQuery=[T#|PovYear|.base])

It will create a list like this one:

S#Actual:T2021M1, S#Actual:T2021M1, .. ,S#Actual:T2021M10,S#Budget:T2021M11,S#Budget:T2021M12

I didn't test both functions, but both concepts will work.

Why simple if you can solve it complicated?

Here is the simple solution: T#POV.AllPriorInYear:S#Actual, T#POV:S#Actual, T#POV.AllNextInYear:S#Budget

you can find it here:

The other concepts might be helpful in more complicated situations.

Just piggy backing off of Christian's last comment/solution, you can also have T#POV.AllPriorInYearInclusive:S#Actual, so could skip the T#POV:S#Actual.