Once the Terminal displays "Install finished successfully" , open your folder to find the Install macOS Catalina.app file.

Disclaimer: macOS Catalina is an older operating system and may not be suitable for all users. This guide is provided for informational purposes. Always ensure compatibility with your hardware and software before proceeding with any installation.

This can happen if your Mac is running an older version of macOS that does not trust the installer’s signature. Try temporarily disabling Gatekeeper:

Terminal (softwareupdate) — useful for scripting or if App Store link doesn’t work