If you build something outside of the snapcraft build process, it is essential that you use a similar environment matching the base: you picked and then also make sure to use a correct DESTDIR variable to install it into its own location, not on the host…
TBH, I’d just take the original snapcraft.yaml and update it to core22 (the original still uses core18 which corresponds to an 18.04 build environment) and bump all the necessary stage and build-package versions as well as moving to new snapcraft schemas … and then let snapcraft do the build
For the schema changes there is: