Question is, how to do it when using the dash bootstrap component? Must be quite simple I guess, but I do not exatly understand how to do it. Not that much doc. Or I didnt find it, unfortunately
Inspecting the .scss code I find
.navbar-toggler-icon {
background-image: $navbar-dark-toggler-icon-bg;
}
but no clue what I can infer from that
dash-bootstrap-components uses Bootstrap 4 which dropped support for the glyphicons that were in Bootstrap 3. The default icon is defined in the CSS here, you could try overriding that.
Alternatively you should be able to create your own toggle using a Button component and then adding the navbar-toggler classes to style it + a FontAwesome icon of your choice.