We have an app which is not allowed for the app store as it stated we need a custom app as the app is for an internal usecase only. The client has employees in France, Germany and Switzerland. They all have an own device (BYOD). Custom Apps Redeem Codes are for one country only. How can make the apps available for all of them without the hassle of an enterprise distribution (we don't have managed devices).
Custom Apps in Europe for international employees
There is a new option called "Unlisted app distribution", which might suit your case.
The app is not listed on the App Store, and is made available by distributing a direct link.
See: https://developer.apple.com/support/unlisted-app-distribution/