How to Install latest mac os catalina, to the older laptop
- Download the latest version of the Catalina patch here. Open the Catalina Patcher app.
- Click Continue.
- Choose Download a Copy.
- The download (of Catalina) will start - since it's almost 8GB it is likely to take a while.
- Plug in a flash drive.
- Choose 'Create a bootable installer' from the options.
- Plug the bootable installer into the Mac you wish to update.
- Restart the Mac while holding the Option/Alt key. This will cause the Mac open in Startup Manager.
- Choose the bootable installer drive and Enter.
- Now your Mac should open in Recovery.
- Choose Reinstall macOS and wait for the new version of macOS to install.
- After the installation has completed, you should restart the Mac in Recovery mode again, choosing the drive that contains the bootable installer.
- Now choose macOS Post Install and the required patches will be installed on your Mac so that Catalina can work.
- When the patches have been applied to choose Force Cache Rebuild.
- Restart.
I also suggest you go through this video.