Simial problem with my Mac book air 2014 with 30 GB free. Find some cache for old devices in xCode and delete them. Now + 10GB and update is going. alternativly use app by Kolakowski. It does the same job. https://apps.apple.com/us/app/devcleaner-for-xcode/id1388020431?mt=12 Very sad to see that 40GB needed to install 5GB.