Idea needed to stop cell from calculating to preserve its value

As far as VBA involvement goes, this Module is kind-of cute:

Option Explicit

Dim liveMap As New Dictionary

Public Sub sweepDictionary(sn As String)
    If liveMap.Exists(sn) Then
        Dim d As Variant
        Set d = liveMap(sn)
    
        Dim k As Variant
        For Each k In d.keys
            Dim addrCache As Variant
            addrCache = Split(d(k), "!")
            Worksheets(addrCache(0)).Range(addrCache(1)) = Range(k)
        Next
    
        liveMap.Remove sn
    End If
End Sub

Public Function ifCache(aBool As Boolean, thenLive, elseCache) As Variant
    If aBool Then
        If Not liveMap.Exists(thenLive.Parent.Name) Then
            Set liveMap(thenLive.Parent.Name) = New Dictionary
        End If
        
        liveMap(thenLive.Parent.Name)(thenLive.Address) = _
            elseCache.Parent.Name & "!" & elseCache.Address

        ifCache = thenLive
    Else
        ifCache = elseCache
    End If
End Function

Needs to be augmented by a basic invocation code inside every Worksheet object that wants to use ifCache:

Private Sub Worksheet_Calculate()
    sweepDictionary Me.Name
End Sub

With that scaffolding in place, it is now possible to produce the desired functionality:

G5 = ifCache(F4,F5,F6)

F5 sits in the calculation tree and F6 receives a copy for as long as F4 is TRUE.  G5 receives F5 so long as F4 is TRUE, otherwise F6.

But it does require the spreadsheet receiver to enable VBA.  So if there were a Lambda solution, that would be preferable.