Replacing the Druplicon favicon in a custom theme for Drupal 8
Placing the favicon.ico in the root of the theme folder, presuming you are using a custom theme, is by far the easiest way to tell Drupal to use that favicon.ico file in the rel shortcut icon (favicon) tag— and so displayed by modern browsers in the tab bar.
Found and elaborated on the answer here quite some time ago:
Added the answer here also:
Might want to add the answer here...