You can download macOS Catalina 10.15.7 from the Mac App Store or through the Software Update mechanism. Here are the steps:
Open and change the system date back to a time when the certificate was valid: macOS Catalina 10.15.7 Download Hub. 1 de out...
softwareupdate --fetch-full-installer --full-installer-version 10.15.7 Use code with caution. You can download macOS Catalina 10