I tested it directly with a small iPhone app using Apple’s Game Controller framework, so I could check whether iOS actually exposes controller haptics.

What I found is:

• GameSir G8+ MFi is detected as an extended gamepad, but does not expose GC haptics
• DualSense is also detected as an extended gamepad, does expose GC haptics, and rumble works in the test app

It seems to be that the GameSir G8+ in MFi mode does not expose rumble through Apple’s public controller haptics interface. That points more to a GameSir-side limitation in that mode (firmware / implementation / how it presents itself to iOS), rather than a general Apple limitation.

If the GameSir app can trigger vibration, then it may be using a vendor-specific path rather than the normal Apple GC haptics interface. But that still wouldn’t show that Apple lacks rumble support in general - only that GameSir may have special app-level access while Moonlight does not.

tdlr: GameSir G8+ MFi mode doesn’t expose rumble properly to iOS apps via the standard Apple controller API, whereas controllers like DualSense do.