The answer is that (approximately) every ad you see is targeted based on (approximately) everything you've ever done on the Internet, every purchase you've made in-person or online, and every location you've been to physically.
I don't think attaching a disclaimer like this to every ad will be impactful at all.
If it's more visible how pervasive it is to your average person who might not think very much about it, there might be louder demand for it to change. Or everybody will just begrudgingly accept it because they don't want to give up their TikTok, who knows, but I still think it should be more transparent. And maybe if a company has to attach "Disclaimer: this ad is provided by gross violations of your privacy" to their ads like the health warnings on a pack of cigarettes when they choose to advertise that way, they'll choose to not do it that way.
I'm sure there's some flaw in my logic here but I'm not the only one who thinks something's got to change.