I have a 2017 Macbook Air with MacOS Sierra operating system. Do newer versions of MacBook Air offer more security

While newer hardware can add hardware-specific features adding to security, the big jumps are running newer software and as having a computer capable of running the latest Mac operating system. Sierra is quite old.

Read this article about installing a newer system version on your computer. A 5 year old computer should be able to run a system version that is still receiving updates from Apple:

Update macOS on Mac - Apple Support

A 2017 MacBook Air can upgrade to Monterey. Monterey is still receiving security updates. Sierra is not. So I should upgrade to Monterey as soon as possible

So you don't need a new MacBook, as this MacBook is still supporting recent software and security updates