Don’t know if a relevant option was added later or maybe it’s not considered supported, but I’ve found a way to skip copying the libraries. Define a custom build setting for a target: OTHER_SWIFT_STDLIB_TOOL_FLAGS Set it to: --source-libraries /dev/null This will effectively disable copying the Swift libraries. I’ve found the option by running this in Terminal: xcrun swift-stdlib-tool --help

I wish they would announce it in release notes. From https://bugs.webkit.org/show_bug.cgi?id=216593 : The world apparently isn't ready for macOS 11.0 in User Agents. Because of the depressing UA sniffing code on the web, let's just report our current shipping release until things settle down. https://trac.webkit.org/changeset/267148/webkit

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