When you update to a new version of Xcode, you can often be left with older versions of the simulator hanging around. You can find out which simulators are unavailable by browsing the results of this query:

xcrun simctl list devices

You might see some output like this:

-- Unavailable: com.apple.CoreSimulator.SimRuntime.iOS-14-5 --
    iPhone 8 (random UUID) (Shutdown)

You can delete any unused simulators and reclaim the space on your machine:

xcrun simctl delete unavailable

I previously linked to a great resource full of Simulator tips and tricks which is also really worth a read.

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