You are looking at a Petalinux project and want to know which Petalinux version it uses.
Inside every Petalinux project, in addition to the "build," "components," and "project-spec" directories, there's also a hidden ".petalinux" directory.
Inside .petalinux, a file named "metadata" contains the Petalinux version on the first line.
$ ls build components config.project image project-spec $ cat .petalinux/metadata PETALINUX_VER=2021.2 ...
This file has existed since at least Petalinux v2018.1, if not since before then.