Why can't I upgrade Macbook Air from Catalina 10.5.1 to 10.5.4?

Some versions in hardware, can run a beta version for awhile, in older Mac; & then

later on the newer actual retail release is beyond the capability to run in that Mac.

(thought I'd seen this earlier, been busy offline)

first post: Why can't I update Macbook Air from Catalina 10.5.1 beta to a newer version?

https://discussions.apple.com/thread/251590766

• How to erase a disk for Mac - Apple Support

https://support.apple.com/en-us/HT208496

• How to reinstall macOS from macOS Recovery - Apple Support

https://support.apple.com/en-us/HT204904

So as alluded to elsewhere, you may consider larger SSD (as size & format concerns)

..depending on the age and build/year identification of the MB/Air you have now..

Or see if the reinstall instructions - above - can make go & Sell it.

{Noted your Duplicate post after posting to both!}

Take care & good luck!☀️🎣