1 -Create a USB bootable
Use this tool and download Catalina or Big Sur from Apple servers
installScript_1016fullapp.zip
Credits: crazybirdy
Copy Catalina / Big Sur installer to Applications folder, open terminal and run
Catalina
Big Sur
Monterey
If you want check one step by step, check here
-Opencore Vanilla Tutorial
https://tinyurl.com/y2dmt5af