I mean, you can use custom search engines, but the only way to get them on android is to sync them over from a desktop install.
It's such a strange kludge, especially if you a) don't use desktop vivaldi or b) don't use sync. Maybe one day they'll add in the menu item or whatever. It's getting better but Android Vivaldi has been getting like one new feature a year it seems like.
Vile. Disgusting.
I feel so bad for the minority of people there. But the majority apparently, instead of seeing "fuck yeah, Kamala, she could be beacon of democracy and progress in the world" decided "nope, orange man hate people me hate so FUCK YOU OTHER PEOPLE".
It's so sad.