You have two possibilities:
1. In the B4XProgressbar module, set mBase as Public
Public mBase As B4XView 'ignore
And then in the main code:
B4XProgressbar1.mBase.Visible = False
2. Add the Visible property in the B4XProgressbar module.
'sets or gets the Visible property
Public Sub getVisible As Boolean
Return mBase.Visible
End Sub
Public Sub setVisible(Visible As Boolean)
mBase.Visible = Visible
End Sub
And then in the main code:
B4XProgressbar1.Visible = False