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$ xcrun simctl listapps booted | grep group.com.apple.FileProvider.LocalStorage
"group.com.apple.FileProvider.LocalStorage" = "file:///Users/<user>/Library/Developer/CoreSimulator/Devices/<UUID>/data/Containers/Shared/AppGroup/<UUID>/";

上のフォルダーの中にあるFile Provider StorageフォルダーがファイルアプリのこのiPhone内フォルダーになる

参考: Solution: How to get files in Files app in iOS simulator | by Stephen Lee | Medium