TL;DR: Reddit is removing the option to opt out of ad personalization, targeting ads based on user activity. Some specific ad categories can still be limited, but there’s no more opt-out option.
Who views ads in Reddit? Except for all the shill posts, that is.
I’m pretty sure it’s everyone who uses their app, since every third post and every fourth comment on it is an ad of some sort (or at least that’s how it seemed). I’m sure anyone on old.r with an adblocker is unaffected but during the brief time I had their app installed there were enough ads to render it unusable and unnavigable.