How to install MacOS Catalina

The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. Make sure to use Only Safari to commence the download as Other may not work

Once Catalina is download and in the Applications folder - suggest stop there and do a Time Machine Backup. Disconnect all external drive after TM Backup and shutdown the computer. Restart and Immediately hold the SHIFT key. This is Age Mode which does a Repair Disc, clears cache files and only loads Apple Software. It will load slowly - normal. Log in and then run the Catalina Installer. Follow the prompts and there might be several automatic restart until the final reboot and Setup Assist of Catalina will be presented.

Make a Time Machine Backup Before attempting. Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina and Big Sur Only support 64 bit and there is not workaround.

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation.

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How to get old versions of macOS - Apple Support