Failure to update my MacBook Air..

Manually download the Catalina Combo 10.15.7. Once downloaded, check and make sure the internal drive has 20 + GB Empty Space. Start charging the MBA, Restart in Safe Mode ( SHIFT Key at startup ) Run the Installer. It may require several automatic restarts. Be patient and give it time to process,

To be safe, Before doing the installation, make a Full Time Machine Backup and maybe a good Bootable Cone.

Do I presume you already tried the earlier instruction ?? You have not mentioned they worked or did not !! One you do that, we can help but need addition info like error messages presented and if so what were they saying ?

I did try all the recommended actions and finally able to download the latest version of Catalina and was able to get the update that way. MyMacBook Air was not actually shutting down when I hit restart until I downloaded to new version of OS.

I can't install the update to new macos catalina 10.15.7

what macOS version are you running?

What version of macOS are you running?

So the instructions worked. Good to hear that. Enjoy