https://wccftech.com/macos-10-15-5-bug-preventing-users-from-creating-bootable-backups/

Apple seeded macOS 10.15.5 update to all users earlier this week that housed the new Battery Health Management tool for MacBooks that aids to extend the battery lifespan. Apart from this, the build also carried several bug fixes and performance enhancements which would improve the user experience of users. However, that's not likely the case because it looks like the latest release brought forward a bug which is preventing users from creating a bootable backup of macOS Catalina using the app.

As we have mentioned earlier, a macOS 10.15.5 bug is preventing users from creating bootable backups. The bug is not new as it was also previously present in the beta release of the build as well. The bug exists in the AFPS volume in macOS Catalina 10.15.5 and fortunately, it is only affecting new backups on Macs that are on the latest macOS 10.15.5 build. Existing backups made on macOS 10.15.4 and lower will not be affected.