Technically speaking, uBlock origin is not strictly an ad blocker. It is a general purpose content blocker; it will block whatever content is matched by its block lists; and it happens to ship with ad lists enabled by default.

Of course, practically speaking it doesn't just "happen" to block ads; that's a major motivation for its development, and so we usually just refer to it as an ad blocker.

To answer your question directly: if you want ads and no cookie popups, disable the ad lists and enable the cookie popup list.

Yes, at that point you may as well just install the other addon, but the uBlock method preserves a key advantage: the ability to combine multiple cookie popup block lists. This is useful in case several people are making lists that cover different corners of the internet.

Tangential question, but I would love to know if a group of people who prefer ads but not cookie warnings exist? Do they rank supporting the website above minor inconvenience of pop-ups and advertisements? That's gotta be a unicorn in terms of internet users.

Whitelist the good sites? Given that the vast majority of sites run garbage and/or intrusive ads, auto-playing videos, etc. and I don't really care about supporting most of them, a blacklist-first approach makes sense and I just whitelist the very few on which I'll accept ads.

You can use sites that are supported by ads just fine with adblock. Why couldn't you?

You'd still be better to use uBO since it's the more actively developed software.

Using sites that are infested by ads is the very reason to use an ad blocker.