Apple offers a nice List of Entitlements and Entitlement Key Reference that anyone can use.
But there also exist some "custom entitlements" that you can only use if your app identifier was whitelisted for their usage.
3 examples:
com.apple.developer.passkit.pass-presentation-suppression
= Suppressing the Display of Apple Pay Passescom.apple.developer.payment-pass-provisioning
= Enabling In-App Provisioning of Payment Cardscom.apple.developer.networking.HotspotHelper
= Register an app as a Hotspot Helper
The first two are actually listed via the Key Reference on Apple Pay and PassKit Entitlement Keys, but the third is only listed on some code documentation (see yellow box).
What kind of custom entitlements do exist?