If you check Xcode logs, you’ll find that downloads.developer.apple.com is throwing 403 Forbidden errors when you try to get the list of simulators, or try to download a symbols dmg. Either Xcode 12.0.1 is using the wrong URL, or the server is misconfigured. I’ve filed feedback (FB8748190) and encourage everyone to do the same.

I’ve run into the same problems. If you look at the Xcode logs, downloads.developer.apple.com is throwing 403 Forbidden errors. Either Xcode 12.0.1 is pointed at the wrong server/directories, or the server is misconfigured. I’ve filed feedback, and encourage everyone to do the same. Hopefully we’ll see a correction soon.

I'm seeing the same with Xcode 12.0.1. I'm unable to download watchOS 7.0.1 symbols. I'm also unable to prep devices running iOS/iPadOS 14.0.1 for development, and I'm unable to get a list of simulators in the Components pref pane. All of these issues stem from download.developer.apple.com rejecting my dev credentials. My account is in good standing, so this is either an issue with Xcode 12.0.1 or with Apple servers. I've filed feedback: FB8748190