While this is a commonly held believe in many corners it doesn't appear to be well backed by data & research. Freakonomics also covered this topic in some detail recently.
Some examples where it's proven untrue:
Nytimes drops targeted advertising in Europe: https://digiday.com/media/gumgumtest-new-york-times-gdpr-cut...
>“The fact that we are no longer offering behavioral targeting options in Europe does not seem to be in the way of what advertisers want to do with us,” he said. “The desirability of a brand may be stronger than the targeting capabilities. We have not been impacted from a revenue standpoint, and, on the contrary, our digital advertising business continues to grow nicely.”
Danish broadcaster grew revenue after dropping targeted ads: https://techcrunch.com/2020/07/24/data-from-dutch-public-bro...
>The data shows the NPO grew ad revenue after ditching trackers to target ads in the first half of this year