If you regularly use YouTube from a browser on a desktop/laptop, you should be familiar with overlay ads. These are banner-style pop-up ads that normally appear at the bottom of the video playing, and more often than not obscure parts of the video currently being watched.
In a new development, YouTube has confirmed that this kind of adverts will be retired starting April 6, 2023. This was done in an official YouTube forum post where Google refers to the ad as a ‘legacy ad format’ and acknowledges it has been ‘disruptive for viewers’
“Starting on April 6th, 2023, the “Overlay ads” ad format will no longer appear on YouTube to help improve the viewer experience and shift engagement to higher performing ad formats on desktop and mobile devices. Overlay ads are a legacy ad format that only served on desktop and are disruptive for viewers. We expect to see limited impact for most Creators as engagement shifts to other ad formats,” says YouTube’s statement on overlay ads.

It makes sense that the company notes that getting rid of the overlay ads will only have a limited impact on YouTube creators, primarily because the format was only used on desktops and nowhere else. It stands to reason that this constitutes a tiny percentage of revenue a given channel generates.
To this effect, starting April 6, YouTube creators will also not have the ability to activate the overlay ads from within YouTube Studio when tinkering with the monetization options.
YouTube does not expound on what other ad formats overlay ads would be replaced with, however, a product tagging feature has been theorized where creators would be allowed to tag products they are using or talking about in their videos.
It will be interesting to see what YouTube comes up with to replace the banner ads. The company has already come under fire in the recent past, front-loading a lot of unskippable ads (up to 10 in some experiments) before your selected video starts playing.