Source? Is there any non-Apple app that has this entitlement?

If your app happens to be a browser that's only usable in the EU then:

https://developer.apple.com/documentation/browserenginekit/p...

I believe the Delta emulator has JIT support, but possibly only when installed as a developer.

As far as I can tell, you need to connect your phone to a PC running software which enables JIT by exploiting a feature intended for remote debugging. https://faq.altstore.io/altstore-classic/enabling-jit