gtk_assistant_remove_action_widget() fails when header bar is used
Look at the code: https://gitlab.gnome.org/GNOME/gtk/-/blob/5f8ab17a0cbd8917fd05073636f7ccc8d01bd4fd/gtk/gtkassistant.c#L1985
There is no condition for the header bar, which is there for the gtk_assistant_add_action_widget
(involving add_to_header_bar
function).
The result is that the button is not removed when the header bar is used.