setting `MACOSX_DEPLOYMENT_TARGET` does it require the sdk?

[ipatch]

when working with cmake based projects i see some references while doing searches to set the below cmake/env var

MACOSX_DEPLOYMENT_TARGET

i've recently started setting that var (cmake) with -DMACOSX_DEPLOYMENT_TARGET="10.9" per this

i'm setting this var because i am publishing releases for older versions of macos and setting that var allows me to run my app bundles ie. MyProject.app on big sur, catalina, and mojave.

my question do i need to download the 10.9 SDK and set that up, or is the current version of xcode installed on big sur able to use that var with cmake without having to download install the older sdk?

thanks for making this github repo BTW 🙏