Improved "find duplicates", but conditional formatting not working - vba

Question

I'm looking to use conditional formatting to mark duplicates, but I want to look for duplicates in multiple columns and mark the entry regardless of which column the duplicate is located in. This is not natively supported in any way I've found, so I made my own UDF. Code listed at the bottom of this post.
The problem is that while the UDF works as expected, I cannot get the CF to work.
I have a CF where I'm formatting some cells based on the value in the same row but different column, and I've used the formula =INDIRECT("Z" & ROW()) <> 0 with great success to achieve this. Building on this, I tried the following for my UDF:
=findCandidatesForDuplicate(ADDRESS(ROW(); COLUMN(); 4))
=findCandidatesForDuplicate("B" & ROW())
But this code does not give any formatting - none whatsoever. The applied range is $B$2:$B$4000, since that's the only range I want it to mark. I've tried changing the UDF and the CF input between passing strings to passing ranges, but nothing I do will get it to apply the formatting.
I assume since formatting is not applied, that the UDF is not run on the intended selected cells, which again I assume is caused by not being able to make Excel understand how I want it to parse the CF input.
In the Worksheet, for row 14 which I know is a duplicate, I can input =findCandidatesForDuplicate("B14") and the cell will show TRUE.
Likewise, I can input =findCandidatesForDuplicate(ADDRESS(ROW(B14); COLUMN(B14);4)) and it will also show TRUE.
The question then boils down to this: how do I make the conditional formatting engine understand what I want to do (which is run this UDF with every cell in the range the rule is applied to as an argument and mark the corresponding cell in column B)?
Here's the function code. Basically a row is regarded as a duplicate if it finds duplicate entries in any of the columns listed.
Function findCandidatesForDuplicate(rngStr As String, Optional countOnly As Boolean, Optional dbg As Boolean) As Variant
Dim rng As Range
Dim colA As Range, searchString As String, result As Long
Dim ws As Worksheet, tbl As ListObject
Set ws = Application.ThisWorkbook.Worksheets(1)
Set tbl = ws.ListObjects("Tabell1")
Set rng = ws.Range(rngStr)
Set colA = Range("A" & rng.Row)
For i = 3 To 5
searchString = colA.Offset(0, i - 1).Value
If searchString = "" Then GoTo NextIteration
'Set rng = Range(rng.Address, tbl.ListColumns(i).DataBodyRange.Address) ' Only searches downwards from input range
Set rng = Range(tbl.ListColumns(i).DataBodyRange.Address) ' Searches the entire column
result = Application.WorksheetFunction.CountIf(rng, "=" & searchString)
If result > 1 Then
If dbg = True Then Debug.Print "Found result in loop no. " & i - 2 & ", matching on value " & searchString
Exit For
End If
NextIteration:
Next i
If countOnly = True And result > 1 Then
findCandidatesForDuplicate = result
ElseIf countOnly = True Then
findCandidatesForDuplicate = 0
ElseIf result > 1 Then
findCandidatesForDuplicate = True
Else
findCandidatesForDuplicate = False
End If
End Function

Answer 1

I haven't found why this doesn't work, nor how to make it work, so here's a workaround:
Populate some far-off column with the UDF calling its own row, then use =INDIRECT("AAA" & ROW()) = whateverValueSetByUDF as the formula to make CF show selected formatting on the cells that trigger the UDF.
It's unelegant and requires a column-wide, manual text-to-column update on the column containing the UDF results every time something changes (filtering the table will work fine, but if you change the sorting you have to update as described)... but it works as long as you know how to use the sheet.
Also, I revised the code in order to have more options for how to format the rows. With this style of output, you can - in addition to finding the rows which are possible duplicates - highlight which columns are triggering.
Usage: Use the INDIRECT formula as above, tailor to your specific setup. I recommend setting = or <> to one of the resultWhereString values.
Function findCandidatesForDuplicate(rng As Range, Optional countOnly As Boolean, Optional dbg As Boolean) As Variant
Dim colA As Range, searchString As String, result As Long, resultWhereString As String
Dim ws As Worksheet, tbl As ListObject
Set ws = Application.ThisWorkbook.Worksheets(1)
Set tbl = ws.ListObjects("Table1")
Set colA = Range("A" & rng.Row)
For i = 3 To 5
searchString = colA.Offset(0, i - 1).Value
' --> You can add more criteria here
If searchString = "" Or searchString = "myEmail#domain.com" Then GoTo NextIteration
Set rng = Range(tbl.ListColumns(i).DataBodyRange.Address) ' Searches the entire column
result = Application.WorksheetFunction.CountIf(rng, "=" & searchString)
If result > 1 Then
If dbg = True Then Debug.Print "Found result in loop no. " & i - 2 & ", matching on value " & searchString
Select Case i
' --> Update this loop if the range of i changes
Case 3
resultWhereString = "ResultCol1"
Case 4
resultWhereString = "ResultCol2"
Case 5
resultWhereString = "ResultCol3"
End Select
Exit For
End If
NextIteration:
Next i
If countOnly = True And result > 1 Then
findCandidatesForDuplicate = result
ElseIf countOnly = True Then
findCandidatesForDuplicate = 0
ElseIf result > 1 Then
findCandidatesForDuplicate = resultWhereString
Else
findCandidatesForDuplicate = ""
End If
End Function