file provided by Apple for users with compatible older Macs. Apple Support Alternative & Archival Sources

Before downloading, ensure your Mac supports Lion:

If you are performing a clean install or need a backup, you can create a : Mac OS X Lion Installer - Apple Support

The installer certificate expired in 2019. Fix: Set your Mac’s system date back to 2012 before running the installer.

This method is the ultimate fallback. However, it downloads directly from Apple’s servers at a slow pace (sometimes 2-3 hours), and the resulting installer vanishes after installation.