If you're willing to spend the time to learn how to write custom policies, SELinux can be used for this, to some extent. It's highly customizable and can sandbox your apps, but the process of doing so is quite complicated. I wrote a small guide on custom policy management on Gentoo in another comment if you're interested.

There's also apparently a "sandbox" feature, but I don't know much about it. I just write my own policies and make them as strict as possible.

As an example, my web browser can't access my home directory or anything except its own directories, and nobody (including my own user), except root and a few select processes (gpg, gpg-agent, git, pass) can access my gnupg directory.

This only covers security/permissions, and doesn't include many of the other benefits of containerization or isolation. You could also try KVM with libvirt and Gentoo VMs; that works pretty well (despite update times) and I did that for a while with some success.