iOS14 update needed to download apps.

A MacBook Air can't run iOS at all. iOS is for iPads and iPhones. Any Mac would be using macOS.

Going from your tagline, Monterey, 12.6 is likely the last version of macOS your MacBook Air can be upgraded to. In order to get a newer OS, you're going to have to invest in a new, or newer Mac.

If you are seeing an app that requires "iOS" then it is an app for an iPhone only. Sometimes I see apps not suited for a computer if I am using a browser.

macOS Sonoma is compatible with these computers - Apple Support

macOS Sequoia is compatible with these computers - Apple Support

No Intel-based MacBook Air is compatible with Tahoe.

Developers chose which OS version they want to continue and support. Many will allocate their resources to just concentrate on the new versions of the OS and not spend the time and money to continue and support the ever dwindling user base found in earlier versions.

Your OS would not be able to be updated on a Mac that does not have the hardware capabilities to support a newer versions. You can imagine the uproar if you updated the Mac and the OS just caused constant crashes because it does not have enough RAM or the speed of the processor is too slow to run it without a problem. Software has always outpaced Hardware ever since the first computer because the Hardware is fixed.