In June 2008 Apple announced Mac OS X Snow Leopard, proudly boasting that it would have "no new features". Instead of piling on new things, Snow Leopard aimed to build on the success of its predecessor, Leopard, opting to focus on under-the-hood performance and stability improvements throughout the system.
I think that is the version my MacBook Air shipped with in 2018. Maybe it was 10.13 and updated to 10.14 right after I got the MBA.