Easy. Get moneytization on and wait for a few days.

Everyone with moneytization is regarded a youtube partner due to a new policy.banner and such are unlocked through performance.

What if I don't want to monetize?

You look like the kind of person who requires Adblock in his life.

Then you are screwed. No moneytization , no custom thumbnails as far as I know or you need to use a program or something which calculates what thumbnails youtube will suggest due to the duration of tge vid and swap thatspecific frame with the pic you want,however this is annoying if not scaring the shit outta your viewers

or you could partner with a network if u meet the requirements for it etc.

In the video, it showed that there were advertisements everywhere. Download Adblock, and that should take care of all of those pesky ads :).