YouTube is currently working on updating the terms & conditions of its services, allowing Google to display ads on non-monetized content.
According to the official YouTube Blog, Google has confirmed that those who are not affiliated with the YouTube Partner Program will try to display ads on uploaded videos.
In other words, if you do not make money from your YouTube content, Google owns the money for the ads that appear on your YouTube video and you do not receive any money from this.
If you do not make money from the videos you add to YouTube, Google will make money by showing ads on it, usually, a portion of that money goes to the relevant content creator, but here Google owns the entire amount.
The official YouTube Blog has announced that the new rules will take effect outside the United States by mid-2021.