[DiapDealer]

We did not remove the Launch External Html Editor button/icon from Sigil. The icon changed sometime after Sigil 0.9.15, but unless you hid that toolbar, the functionality for launching PageEdit via that button is still there. It now looks like an 'X' comprised of a blue slash and a pencil in the most recent versions of Sigil. But if you're still using Sigil 0.9.15, it's more likely that you've just accidentally hidden the "Edit" Toolbar. Use the View->Toolbars menu to recheck the "Edit" toolbar and the icon will reappear. The keyboard shortcut should still work for that feature even if the toolbar itself is hidden.

I do not know anything about Stephen Outram--nor do we endorse any third-party instructional videos regarding Sigil--but you should know that Sigil version 0.9.15 is outdated and unsupported. You're quite welcome to stay with the older version if it suits your needs, but you're not as likely to get as much support as you would with recent versions.