- Chrome (mind you, I don't have it installed, so this would send me to the AppStore)
- the "Google" app (again, not installed)
- Safari (which does not open Safari, rather an in-app WKWebView, so that Sundar can still milk your precious eyeballs)
- and finally at the bottom the "Default browser app" (this is what you want)
Of course, there's no setting to save this choice once and for all, so this is done each and every time you try opening a link in the YouTube app. Wait, actually, I'm 99% sure it would suddenly remember your choice if you had installed one of their browsers. From that moment they would duly open all links in Chrome/Google, without this annoying prompt.
I bet every Google app does this on iOS to get you install their crap. Disgusting practice.