But Apple would only be losing the monopoly in the EU. The theoretical maximum amount this could cost Apple is 100% of EU app store revenue.

If Apple pulls out of the EU, they will definitely lose that EU app store revenue, and will additionally lose all EU hardware revenue.

Apple would be showing weakness by capitulating to European regulators, creating a real risk other countries would follow.

Apple already showed weakness capitulating to China debatable demands in exchange for revenue, multiple times.

"Apple tells suppliers to use 'Taiwan, China' or 'Chinese Taipei' to appease Beijing" https://www.theregister.com/2022/08/05/apple_warns_suppliers...

"The problem with canceling Jon Stewart: Apple bowed to Chinese government censorship" https://www.usatoday.com/story/opinion/voices/2023/10/26/jon...

"Apple pulls Taiwanese flag emoji from iPhones in Hong Kong" https://www.latimes.com/business/story/2019-10-08/apple-taiw...

Even Google didn't went that far and withdrew from China.

"In early 2010, Google shut down its Chinese website altogether after failing to reach an agreement with Beijing over how much content to censor in search results." https://observer.com/2022/10/alphabet-shut-google-translate-...

I believe giving into China was a mistake for Apple executives ethically, commercially and politically.

In the long term they’ll be forced to give up all the commercial surpluses to local mega apps by the government, and the political/ethical problems require no elaboration.