How to create youtube overlays?
EDIT: Upon further research, this only seems to be available to high-tier YouTube Creator accounts. I haven't been able to find an example of this from an account with less than 1M subscribers. Here's the Creator tier levels:

https://www.youtube.com/yt/creators/en-GB/benefit-levels.html?noapp=1

ORIGINAL: This is a feature called "Cards" on YouTube. Your account must be in good standing to use this. Go to your video and hit "Edit" then navigate to the "Cards" menu. Here, you can add cards and select the content you want to display. Up to 5 can be added on one video at a time. Here's some documentation and a tutorial:

https://support.google.com/youtube/answer/6140493?hl=en

Hope this helps!