Here's how to upgrade MacOS 10.8.5 to Catalina in 2020
I was given a mid-2012 Air 11 that restored to 10.8.5. As of April 2020 that OS version is useless and the App Updates won't help. The answer is two-step and simple as long as Apple keeps the support page alive.
First you download and install Yosemite, then you can use the App Store to get Catalina installed. That's it! But make sure you use the link below and go to Step 4 and download the Yosemite installer., it's not going to appear in updates. Since I was starting with a clean image I just went for it, nothing to backup. IF YOU HAVE FILES PLEASE BACK THEM UP FIRST, HOWEVER YOU DO THAT.
So just go to https://support.apple.com/en-gb/HT210717and in step 4 you will see the link to download the Yosemite installer. Download and go through all the steps to get Yosemite on your Mac.
After that, upgrade to Catalina and you are good to go. Enjoy!
MacBook Air