I find plain Linux namespaces as sufficient for many things, for example:

unshare --map-root-user chroot ~/rootfs /bin/sh

Sure, it might not be able to clone the rootfs for you, but you don't need snapd to install it and it comes as part of util-linux, essentially being part of almost all Linux systems. (https://ilearnedhowto.wordpress.com/tag/unshare/ is a nice introduction.)

Edit: https://ericchiang.github.io/post/containers-from-scratch/ is also interesting.