Then don't use this particular app? This already exists today: A lot of apps are android-only, or jailbreak-only. In the same sense, tomorrow we'll likely have amazon-store-only apps.
In practice I doubt many apps will use a third-party appstore. Apple has a lot of leeway in how they will implement the regulation - they can make it painful enough to use a third-party store that most popular apps will want to keep using the primary app store to get maximum reach. Just like how almost every android app is on the google play store - despite sideloading being a thing since forever.
In practice I doubt many apps will use a third-party appstore. Apple has a lot of leeway in how they will implement the regulation - they can make it painful enough to use a third-party store that most popular apps will want to keep using the primary app store to get maximum reach. Just like how almost every android app is on the google play store - despite sideloading being a thing since forever.