For sites and apps without (third party) advertisements, it's trivial to use the ads.txt specification iabtechlab.com/ads-txt/ to forbid buying and selling ads on your site / apps. Example:
* grapheneos.org/ads.txt
* grapheneos.org/app-ads.txt
Hit adware developers in the wallet.
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Content-Security-Policy error reporting has never helped me in any way, but it made me very aware of adware extensions injecting ads. No longer make an attempt to use the reporting feature because it's flooded with all kinds of adware errors. Nice to have a way to fight back...