You can now set your preferences to display related videos below YouTube video ads. This extension will allow you to display 2 to 5 related videos. They will appear below the main video when you play it in the YouTube app on your mobile device.
Similar videos can be to add in campaigns that have a Brand and Product Interest or Brand Awareness and Reach goal, and in a video campaign with no goal but with CPV or CPM bid strategies.
Similar videos may not always show your ads. In addition, the number and order of related videos may also change.
Please note, Google Ads will change image requirements for app ad campaigns.
A source: Google Blog