Simulator向けビルドにarmを含めない様にする回避方法がそのissueに書かれてる。 https://github.com/Carthage/Carthage/issues/3019#issuecomment-665136323

Carthage builds fail at xcrun lipo on Xcode 12 beta (3,4,5...) · Is...

carthage install method: [ ] .pkg, [x] homebrew, [x] source which carthage: /usr/local/bin/carthage carthage version: 0.35.0 xcodebuild -version: 12A8169g Are you using --no-build? No Are you using...

1:02 PM

この回避方法を使うと、多分Apple Silicon Mac上のシミュレータで動かないんじゃないかな。