The source – support.google.com
Google reviews related YouTube videos to ensure they meet placement guidelines and ad guidelines. Their status is indicated in the campaign settings in the "Related Videos" section.
They now appear below the main video ad when shown in the YouTube app on a mobile device. There are from 2 to 5 of these videos from the advertiser's channel. These video extensions are now available worldwide to all advertisers using Google Ads.
Similar videos can be added to video campaigns with the goals "Interest in the brand and products" (subtype "Engagement" or "Ad funnel") or "Brand awareness and reach" (subtypes "In-stream with the ability to skip", "In-stream without skip options ”,“ Screensaver ”or“ Announcement sequence ”).
In addition, related videos are available in goalless campaigns with CPV or CPM bid strategies.