@bklynkid Since you can't set it as default the next best thing is to use a keyboard shortcut in the address bar. E.g., s "search query."
E.g., here's my setup
b00d1a2c-6c5b-4cba-bfd4-3dd38bb422ee-image.png
Inflexibility in setting default search is a long-standing complaint. Opera should just exactly copy Vivaldi on this.