Developers outside mainland China, are you required to fill in the ICP number?

If outside China, this is not a requirement.

I will ask this question again for clarification. Developers outside mainland China, are you required to fill in the ICP number in App store Connect?

If your app needs to be listed on the App Store and provide services to users in mainland China, you must fill in the ICP filing number.

Starting from April 1, 2024, apps without ICP Filing Number will be unable to publish updates and face mandatory removal.

The regulations for app filing were newly issued by China’s Ministry of Industry and Information Technology in August last year. For more information on app filing, you can check out the link below.

https://www.appfilingchina.com/blog/app-filing-number-is-needed-for-apps-to-be-listed-on-the-apple-app-store-in-china