is there any upgrade for mac book air os x elcapitan 10.11.

Ingo2711 has the right idea – but I just happened to answer a thread from someone else who appeared to want to upgrade an 11" MacBook Air, and MacTracker indicated that there were a few more 11" MacBook Air models.

To round out the list:

• Mid 2011 models can upgrade to High Sierra, but no further
• Early 2014 models can upgrade to Big Sur, but no further
• Early 2015 models can upgrade to Monterey, but no further

Note that if you upgrade to Catalina or later,

• 32-bit applications will stop working
• iTunes will go away, replaced by separate applications: What happened to iTunes? - Apple Support

Did you already check for available macOS updates, as described in this article?

Update macOS on Mac - Apple Support

If your MacBook Air is from 2010, you should be able to install macOS 10.13.6

A MacBook Air 11' 2012 can be upgraded to macOS 10.15.7

A MacBook Air 11' 2013 supports macOS 11, Big Sur

How to download and install macOS - Apple Support