How does the Eurovision app know where I am from?
As a Chinese living in strict censorship, I use proxy and apple id from various countries. And I often use MITM to capture packets to see the restrictions in the packet. I have to say, Apple’s Privacy Policy is doing a good job. 

1、The app doesn't know which store you purchased and downloaded it from.
2、They can't access the IMEI and UUID directly from the system.
3、They may get your EAP-SIM authentication data from your isp. And your mac address is fixed every time you link wifi. Android is better in this case, you can generate a random mac address.

The most common situation I have experienced is that the app will get your carrier, which is the API provided in iOS. Tiktok Line Apple News even Apple Watch's ECG feature uses this method to identify the user's location. When your sim card is in the phone, whether you use data or Wi-Fi or even in flight mode, the app can get your carrier information.

Another possibility is that your device language is German, and your app will bring Accept-Language: XX-de in your HTTP request header.

And if you use a device for a long time, companies with various apps on your phone may sell information to each other. Large advertising companies such as Google facebook they have enough information to generate a UUID for you.