Unreal is written in C++ but, like Unity, can be scripted in other languages. Like unity it fits the "GC language for high level scripting of non-gc code" pattern. There is certainly no debate about the feasibility of implementing game logic in Lua. Reference counting in graphics drivers is not comparable to GC in Java or C# because its lack of generality permits the use of faster algorithms that don't GC pause. Swift is a workable systems language with reference counting built in, but you should bear in mind that it doesn't have "a garbage collector" per se, like you would imagine when you hear that a language is GC'd.

Reference counting pauses when cascading deletions take place, it well known domino effect.

C# allows for GC free regions with GC.TryStartNoGCRegion, manual memory management via MarshalServices, stackalloc, Span<>() and value types.

Almost forgot Unreal C++ is GC based for entities and anything Blueprint related.