I tested the same project out on 2 devices, both running 16.2. On one device the run(_:::) doesn't show up, and when I manual enter the function it says there are extra parameters on spots #2 and #3. On the other device with the same project it compiles. When I right click, and press show definition. The run(:) open in the RealityKit module file. When I right click on the run(:::) function it opens in the RealityFoundation module file. Im not sure why sometimes the run(_:::) doesn't show.

Yes all macOS, iOS and Xcode versions are on the latest public versions. It just seems like Xcode is not able to "find" the correct function, even though it exist in the RealityKit Framework.