With .NET extensibility you can turn-off visibility of Mini toolbar.
For Map Mini toolbar you can do by executing the following statement
IMapInfoPro.ContextMenus.MapMiniToolBar.Visible = false;
And for Layout Mini toolbar you can do by executing the following statement
IMapInfoPro.ContextMenus.LayoutMiniToolBar.Visible = false;
Please note, once you set the Visible property to False, Mini toolbar will no longer be visible, until you set the Visible property back to True.
Thanks,
Rajesh Gupta