Trouble switching to the M1 Mac or Excel in Office16.54

[jvbeaupre]

I just switched to the new Mac (M1 iMac 24", running the latest system) and updated excell to the most recent version 16.54.
Most of my code no longer runs.
It's mystifying that something so simple as the following bombs with an overrun at the end of the loop.
Has anyone else experienced similar difficulties?

Sub a_test_digammad()
   
    For z1 = 1 To 4.01 Step 0.1
    Debug.Print z1, diGammad(z1)
    Debug.Print "---"
    Next z1
End Sub

Function diGammad(x)
diGammad = x
End Function