The MacBook Air (Retina, 13-inch, 2018) originally shipped with macOS 10.4.1 (Mojave). You can update it as far as the latest release of macOS 14 (Sonoma) – but no further. It is not compatible with macOS 15 (Sequoia), and won't be compatible with macOS 26 (Tahoe).
Identify your MacBook Air model - Apple Support
MacBook Air (Retina, 13-inch, 2018)
Newest compatible operating system: macOS Sonoma
I would strongly suggest that you download or update Pages, Numbers, Keynote, and GarageBand – while you still can. Current versions of these applications require some version of Sonoma or better; so I wouldn't rule out Apple raising the requirement to Ventura for any updates that they release after Tahoe comes out.