Have you ever tried to use proot?
It does not use process namespaces, and can run on Android (on Termux with proot-distro).
No, I haven't tried it, thanks for the pointer. It looks like something that could be used by Drop instead of Linux namespaces. I didn't yet encounter any obvious limitation of the namespaces (other that some distros, like Ubuntu, are keeping programs' access to the user namespace creation behind AppArmor allowlist, which makes the Drop installation more involved).
I've used proot in the past but it crashed often, I'm interested in finding other rootless chroot-like projects.