In 2023, the Digital Market Act in the European Union passed, allowing people to install apps on their iPhone from other sources than Apple's App Store. This is now becoming reality with the Fur Affinity app available in AltStore PAL, one of the first alternative App Stores available.

This means that the app can be installed much more easily, without sideloading! For now only people living in the European Union can benefit from it, but other countries are planning similar laws, so there's hope for more freedom on iPhone in other countries in the future.

Check furaffinity.app to know how to install the app through AltStore PAL!
If you live outside of the EU, you're left with sideloading only, which also works but is trickier. You can also check the website for how to install.