macOS Catalina has been released; See Using Daedalus on Catalina (macOS) to read more about how this impacts Daedalus wallet.
If you upgrade or install or reinstall Daedalus wallet on macOS Catalina you will get this error:
Changes to the way that macOS works implemented by Apple in the Catalina macOS.
We do not have an easy workaround for this.
Apparently, this issue is affecting many software products, not just Daedalus wallet. We will post a solution on this page when we have one.
Read more from Apple about the Notarization Requirement for Mac Software
See also Known Issues