Macro to convert lists in a row to multiple rows with single items

Assuming your data is in A1, Sheet1, then try:

Sub foo()
    Dim l As Long
    Dim s1 As String
    Dim s2() As String
    Dim i As Integer
    
    With Sheet1
        For l = .Cells(Rows.Count, 1).End(xlUp).Row To 2 Step -1
            If InStr(.Cells(l, 2), ",") > 0 Then
                s1 = .Cells(l, 1).Value
                s2 = Split(.Cells(l, 2), ",")
                .Cells(l, 1).Resize(UBound(s2), 1).EntireRow.Insert
                For i = LBound(s2) To UBound(s2)
                    .Cells(l + i, 1).Value = s1
                    .Cells(l + i, 2).Value = Trim(s2(i))
                Next i
            End If
        Next l
    End With
End Sub

An alternative:

Highlight column A. Click on Data on the Ribbon. Choose Text to Columns. Delimited. Space and comma.
Then run this VBA code.

Option Explicit

Sub Gil()
Dim lr As Long, lc As Long, i As Long
Dim lr2 As Long
Dim s1 As Worksheet, s2 As Worksheet
Set s1 = Sheets("Sheet1")
Set s2 = Sheets("Sheet2")
lr = s1.Range("A" & Rows.Count).End(xlUp).Row
s1.Range("A1:B1").Copy s2.Range("A1")
With s1
For i = 2 To lr
lc = s1.Cells(i, Columns.Count).End(xlToLeft).Column
lr2 = s2.Range("B" & Rows.Count).End(xlUp).Row
.Range("A" & i).Copy s2.Range("A" & lr2 + 1)
.Range(.Cells(i, 2), .Cells(i, lc)).Copy
s2.Range("B" & lr2 + 1).PasteSpecial xlPasteAll, , , True
Next i
End With
With s2
lr2 = .Range("B" & Rows.Count).End(xlUp).Row
For i = 3 To lr2
If .Range("A" & i) = "" Then .Range("A" & i) = .Range("A" & i - 1)
Next i
End With

End Sub