The entire idea of "Oh they'll leave" is ridiculous, an empty threat from billionaires who are afraid of regulation.
The EU has 450M (+80M for UK & similar non-eu countries that are likely to follow the EU on such regulations) population to the US' 350M.
The moment the likes of Google, or Meta, or Microsoft, or whomever else leave the EU, they immediately create a market gap. A market gap that will then in short order be filled with a European company that, because of the population sizes, has a notable comparative advantage to the US tech company.
+ As much as HN's readership loathes to admit it, regulations like this are "Good, Actually". Google's monopolist practices are bad for both advertisers and services showing ads. Any would-be competitor that arises from Google leaving the market would, by virtue of being forced by law to not be so shitty, be the better option.
(And yes, this does also apply to pretty much all of the other big tech regulations as well.)
Like, c'mon. "Monopolies bad" is capitalism 101. Even the US' regulators thought Google was going too far.