Duplicate for #10237. We are aware of the issue since the update was published on the Mac App Store and are waiting for Apple to resolve this issue. There is an error with the sandboxing entitlement permission not being applied correctly to the download from the Mac App Store. As a workaround until an update is available from the Mac App Store, please install Cyberduck from https://cyberduck.io/ which does not show this problem.
Version 6.4.3 is now available in the Mac App Store fixing the issue with “connect failed” errors when attempting to connect due to missing codesigning entitlements. Unfortunately, this was caused by a bug in the Mac App Store processing and signing of application submissions.