why is new pages update incompatible to my Mac

According to the equipment profile listed below your post, your computer is a Macbook Air and your operating system is macOS 10.12 (Sierra): MacBook Air 13″, macOS 10.12

The current version of Pages (and of Numbers) requires either macOS Catalina (10.15) or macOS High Sierra (10.14).

Introduction date and model of your Mac are also factors. You can find the introduction date using About this Mac in the Apple menu.

You can check the requirements for macOS Catalina here: macOS Catalina is compatible with these computers - Apple Support

You'll also find a link on that page regarding upgrading to macOS High Sierra if your Mac is not compatible with Catalina.

Regards,

Barry

b02_09_40 wrote:

why is new pages update incompatible to my MacBook Air 13"?

Perhaps because your MacOS version is too old. What is it?