The oldest online ad format, and still the cheapest reach there is.

Banners on websites and in apps: from a narrow strip above an article to half a screen in a news app. The reach is large and the cost per thousand impressions low, which makes it well suited to building awareness.
The click-through rate on display is well below one per cent in most sectors. That is not a flaw but the nature of the channel: people rarely click on a banner, but they do remember it. So judge display on reach and brand recognition, not on direct conversions.
With third-party cookies being phased out, the emphasis is shifting from who the viewer is to where they are. Advertising next to content that matches your subject works without personal data — and keeps working as tracking is restricted further.
A question or project on this topic?