MacBook Air Disk Utility problem

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 Others may not work

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 no workaround.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, 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

Use this method from Apple to Erase >> How to erase an Intel-based Mac

Then use this method from Apple to Install >> How to reinstall macOS

If you have an Intel Mac, then make sure to select the physical drive to erase. This is especially important if the drive is encrypted or if you are installing macOS 10.12 or earlier since the older macOS is unable to recognize APFS containers and volumes. If you are installing macOS 10.13+, then click "View" within Disk Utility and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility since recent versions hide the physical drives from view by default. The physical drive should be identified something like "Apple SSD....".

If you are installing macOS 10.6 to 10.10, then instead of erasing the drive you need to first partition & format the physical drive using the instructions in this article:

https://www.owcdigital.com/assets/support/support-formatting-and-migration/Mac_Formatting_6-10.pdf

Thanks for the help. I actually had a similar problem but I was able to re-partition the SSD myself and get the OS working again. Before I erased the HD, my Mac was running the latest version of Catalina. After reinstalling it went back to Sierra.

Edit: No updates are showing on the App Store

So how do I upgrade it?