Just to add a little information here as well. I can't debug with Xcode 12.1 GM Seed. If I attempt to, it immediately stops at dyld'__fcntl. This is only happening after updated to BigSur beta 10 and happens on both my iMac and MacBook Pro. I also tried a template project and get the same thing. It appears there's something pretty wrong with BigSur beta 10.
However, Xcode 12.2 beta 3 does seem to work for me.
Fortunately, the "Debug process as root" setting resolves debugging with 12.1.
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Developer Tools & Services
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Xcode
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