OpenCore has been updated to the 0.6.2 release and should now support booting both Catalina and Big Sur.
Diff in changes of config.plist since v5
I'm hoping that this release will finally solve the "prohibited" sign appearing when booting the macOS Catalina installer. The only change in this release compared to v8 is a fix to the VBoxHfs.efi driver.
If you still encounter a "prohibited" sign on booting macOS Catalina with this release, use the older v5 release instead. If that fixes it please let me know in issue #2 . If you are able to successfully boot Catalina with this v9 release (as I am) please let me know there too!