According to this link, you should be able to get a sign in option for sandbox account when performing the first purchase of a development signed app. The documentation says, "In iOS and iPadOS, the sandbox account appears in Settings > App Store after the first time you use the device to attempt a purchase in a development-signed app. There’s no need to sign out of the non-Sandbox Apple ID. Sign in using a Sandbox Apple ID." This is not true as SKProductsRequest doesn't provide any results making the first purchase impossible. I had to actually sign out my original account in settings, sign in with the sandbox account, run the app which now provides results from SKProductsRequest and then perform a purchase which provides the actual sandbox login the link suggests. So in this case I have to login with the sandbox account yet again. After this I can login with my original account and the sandbox account will be available in Settings > App Store.

Ok. However, SKProductsRequest(productIdentifiers: Set<String>) doesn't result in any SKProduct when I'm using ProductID's from App Store Connect that has status "Ready to submit".

Thanks for the answer. I would probably have gotten stuck on deselecting the StoreKit config sooner or later :)