@leocg It’s the newest version downloaded from the website but, please note this is Mac version (my appologies as I have not noticed that this is Windows section). I can open : opera://cast but my browser is not finding my Chromecast device.
Slimjet browser has a feature like that. It has another menu you launch from the toolbar and whatever extension buttons you do not need all the time appear on there. They are usable from there, so that frees up more room for the addresses on the toolbar but still leaves the extensions easily accessible.