There’s several places where this could go wrong.
There’s three places where links are configured to open the default browser - where $1 is the desktop file of the browser to be used.
xdg-mime default "$1" x-scheme-handler/https
xdg-mime default "$1" x-scheme-handler/http
xdg-settings set default-web-browser "$1"
Times ago I wrote a small script to easily switch default browser