This is the most common error when trying to use a downloaded DMG. It happens because Apple’s certificate expired in 2020.
Complete Guide to Downloading the macOS Catalina 10.15.7 DMG File download macos catalina 10157 dmg file hot
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When downloading any files from the internet, be cautious and ensure you're downloading from a trusted source. Malicious files can harm your Mac and compromise your data. This is the most common error when trying