Try doing Replace([Enter Number Seperated By Commas],","," or ")

That doesn't appear to work hmm. This is the code I've made before to do it on a textbox in a search form. This is with VBA, much more advanced, but might give you an idea.

If QuestionType <> "" Or QuestionType <> 0 Then
        If Wh <> "" Then Wh = Wh & " " & "AND" & " "
        
        If InStr(1, QuestionType, ",") Then
            Dim QType
            QType = Split(QuestionType, ",", 5)

            If UBound(QType) = 4 Then
                Wh = Wh & "QuestionType LIKE '*" & QType(4) & "*' or (QuestionType Like '*" & QType(3) & "*' or QuestionType Like '*" & QType(2) & "*' or QuestionType Like '*" & QType(1) & "*' or QuestionType Like '*" & QType(0) & "*')"
            ElseIf UBound(QType) = 3 Then
                Wh = Wh & "QuestionType LIKE '*" & QType(3) & "*' or (QuestionType Like '*" & QType(2) & "*' or QuestionType Like '*" & QType(1) & "*' or QuestionType Like '*" & QType(0) & "*')"
            ElseIf UBound(QType) = 2 Then
                Wh = Wh & "QuestionType LIKE '*" & QType(2) & "*' or (QuestionType Like '*" & QType(1) & "*' or QuestionType Like '*" & QType(0) & "*')"
            ElseIf UBound(QType) = 1 Then
                Wh = Wh & "QuestionType LIKE '*" & QType(1) & "*' or (QuestionType LIKE '*" & QType(0) & "*')"
            ElseIf UBound(QType) = 0 Then
                Wh = Wh & "QuestionType LIKE '*" & QType(0) & "*'"
            End If
        Else
            Wh = Wh & "QuestionType LIKE '*" & QuestionType & "*'"
        End If
        
    End If

Any attempt to manipulate the parameter won't work because Access will always sees the parameter as one single value. For instance, if your query is:

    SELECT * FROM MyTable WHERE MyField IN ([user inputs])

If the user enters 1,2,3,4 , thinking the query will become:

    SELECT * FROM MyTable WHERE MyField IN (1,2,3,4)

But Access will see it as:

    SELECT * FROM MyTable WHERE MyField IN ("1,2,3,4")

which will likely return no result, maybe an error too.

To accomplish the original goal, you need multiple parameters:

    SELECT * FROM MyTable WHERE MyField IN ([input1], [input2], [input3], [input4])

Or you can use VBA to construct the SQL using string concatenation, with the user entering the inputs on a form or something.

Good code Adam but limited to 5 elements.
I would use a loop so more elements can be added without having to modify the code.
This is what I came up with based on your code above.

Dim QuestionType As String, wh As String
Dim QType As Variant, X As Long
QuestionType = "1,2,3,4,5"
    
If QuestionType <> "" Or QuestionType <> 0 Then
    If wh <> "" Then wh = wh & " " & "AND" & " "
    If InStr(QuestionType, ",") Then
        QType = Split(QuestionType, ",")
        For X = 0 To UBound(QType)
            wh = Trim(wh & "QuestionType LIKE '*" & QType(X) & "*' or ")
            wh = Left(wh, Len(wh) - 2)  'remove the trailing 'or'
        Next
    End If
End If

Nice. Yea, in my use ,they wanted the limit to always be 5 so made it easier :P.