Did you ever figure this out? I'm having the same problem.

Well this is interesting. I just created another Apple ID account, and signed in with that, and I don't get these errors anymore. So I guess it's something about my Apple ID. But I don't have the slightest idea how to fix that. Edit: one thing I notice about the Apple ID that doesn't work: when I sign in on the simulator, the "Sign Out" button in iCloud is disabled. I don't know if that's relevant.

I've been fighting this since last month. It first showed up in Xcode 14. If I ran my apps in Xcode 13, CloudKit worked in the simulator. Then at some point, I had to wipe some of the simulators. Once I did that, I started getting these errors in Xcode 13 as well so now my only option is to run on device.

I don't know what happened, but I'm now getting the same errors with Xcode 13 so CloudKit won't work in any simulator. I opened a report and got a request to include a simctl diagnose, which I did, but haven't heard anything back since.

I pulled down Xcode 13, and verified CloudKit syncing works correctly in the simulator, so this appears to be something specific to Xcode 14.