Because you can't just hit "Download" on the App Store anymore, players have turned to archival sites and community hubs: Internet Archive:

To play on iOS using an IPA file, you must use sideloading since the game was removed from the official App Store. While various community-sourced IPA files are available, success depends heavily on your device's iOS version and the architecture (32-bit vs. 64-bit) of the file. Key IPA File Sources

Get ready to join the epic battles in Angry Birds Epic! By downloading the IPA file, you can experience the game on your iOS device, even if it's not available in your region. However, be cautious and only download from trusted sources to ensure a safe and enjoyable gaming experience.

The most beginner-friendly method. It requires a computer to act as a "server" to refresh the app every 7 days.