Can't be installed

Are you trying to update your MBA from macOS Catalina to Big Sur? If so, the support article you came here from should provide you with the steps necessary to do so. Did they not work for you? If not, what have you tried, so far yourself, to resolve this so that we don't try offering potential solutions that may not have already worked for you?

Try this:

Reset SMC How to reset the SMC of your Mac - Apple Support

Reset NVRAM Reset NVRAM or PRAM on your Mac - Apple Support

Restart holding Option to load Safe Mode.

Restart normally and check if you can update now.