macOS has not abandoned its Unix layer, and in fact is still a certified Unix (https://www.opengroup.org/openbrand/register/). However, there is a growing gap between certified Unix and the innovations that *nix-like systems have included in the past decade. macOS has not kept up with Linux and the BSDs in terms of feature parity, resulting in a growing gap between the features that come with modern Linux, FreeBSD, and OpenBSD versus macOS. A minor issue is macOS's BSD-derived utilities being based on late 1990s-early 2000s versions and thus not taking advantage of functionality added in later versions of these BSDs. Other issues include no support for file systems such as ZFS and btrfs in macOS (though I remember when ZFS support was proposed for Mac OS X Leopard), and macOS not supporting FreeBSD jails (https://docs.freebsd.org/en/books/handbook/jails/).