Mac Mini Late 2009 with MacOS Catalina shows this menu when booting up. How should I go about fixing the issue without messing anything up. BTW Catalina isn't supported by my Mac
How to install macOS Catalina on an unsupported Mac
How to Install macOS Catalina on Unsupported Macs - iFixit Repair Guide
How to Install: macOS Catalina 10.15.7 Supplemental Update : r/CatalinaPatcher