What macOS upgrades available for my MacBook Air 2017 running High Sierra?

A 2017 MacBook Air can be updated to macOS 12 Monterey.

click here ➜ macOS Monterey is compatible with these computers - Apple Support

To download and update follow the steps in the link below.

click here ➜ How to download and install macOS - Apple Support

You will however need to verify all your apps and make sure they are all 64 bit as 32 bit apps will not work on any macOS version past 10.14 Mojave.

click here ➜ https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html

If you do have 32 bit apps, you will need to update them to be 64 bit, or find 64 bit replacements for them.

A 2017 MacBook Air can be upgraded to the latest version of Monterey macOS 12 but no later.

Be sure to have a current backup (a good idea even when not upgrading) and see instructions in: How to download and install macOS - Apple Support

Be aware that if you upgrade to Catalina 10.15 or later you will also need to update any non-Apple 32-bit apps. See: https://www.stclairsoft.com/Go64/

or

 https://www.macworld.com/article/232735/how-to-check-if-mac-software-is-32-or-64-bit.html