bubblewrap is linux only and offers a fraction of isolation of a microvm
right chain of tought, but
systemd is the only to truly leverage linux namespaces capabilities, allowing private networks, other rootfs, etc
systemd is not the only thing using linux namespaces. For example, the suggested bubblewrap uses namespaces to allow isolated networks (--unshare-net) and changing rootfs (--bind /mnt/foo /)
bwrap has a lot of sharp edges that can bite you, if you're not aware of them.