Comment 2 for bug 1843612

This bug report is 2 years out of date and is missing key components (information)

On a more serious note, pybind11 is up to date in Debian and on the way to Ubuntu, see:
https://people.canonical.com/~ubuntu-archive/proposed-migration/update_excuses.html#pybind11

embed.h is in the pybind11-dev package.

Also note that Ubuntu generally does not update packages to new upstream versions in a stable release.