catalina, La versione di macOS richiesta non è disponibile.

Hi tazzang, Thank you for using the Apple Support Communities. You've posted a question in the English Community. If you are able to repost your question in English, you may reach a larger audience and have a better chance of receiving a reply. Thanks!

Try running these commands in the Terminal. It helped some users.

sudo softwareupdate -l --all --force --reset-ignored

softwareupdate --reset-ignored