I am seeing a similar issue on my MacBook Pro 2020 (M1), with macOS 13.5.2, Xcode 15 GM, iOS 17.0 simulator. It goes away temporarily after running killall Simulator, but it keeps coming back. Looking at my top processes by CPU usage in Activity Monitor, I see:
diagnosticd - 87.5% - 2:08.25
SpringBoard - 85.6% - 7:27.90
diagnosticd - 67.5% - 6:36.72
UnityPosterExtension - 20.2% - 1:40.86
PhotosPosterProvider - 19.7% - 1:38.08
ExtragalacticPoster - 19.7% - 1:37.34
CollectionsPoster - 19.5% - 1:40.69
chrisbhenderson
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For anybody else trying to work around this, I found that the new XCUISystem works on the iOS 17 simulator. It doesn't work at all on the iOS 16.4 simulator.