I also use bubblewrap to isolate npm/pnpm/yarn (and everything started by them) from the rest of the system. Let's say all your source code resides in ~/code; put this somewhere in the beginning of your $PATH and name it `npm`; create symlinks/hardlinks to it for other package managers:
#!/usr/bin/bash
bin=$(basename "$0")
exec bwrap \
--bind ~/.cache/nodejs ~/.cache \
--bind ~/code ~/code \
--dev /dev \
--die-with-parent \
--disable-userns \
--new-session \
--proc /proc \
--ro-bind /etc/ca-certificates /etc/ca-certificates \
--ro-bind /etc/resolv.conf /etc/resolv.conf \
--ro-bind /etc/ssl /etc/ssl \
--ro-bind /usr /usr \
--setenv PATH /usr/bin \
--share-net \
--symlink /tmp /var/tmp \
--symlink /usr/bin /bin \
--symlink /usr/bin /sbin \
--symlink /usr/lib /lib \
--symlink /usr/lib /lib64 \
--tmpfs /tmp \
--unshare-all \
--unshare-user \
"/usr/bin/$bin" "$@"
The package manager started through this script won't have access to anything but ~/code + read-only access to system libraries:
bash-5.3$ ls -a ~
. .. .cache code
bubblewrap is quite well tested and reliable, it's used by Steam and (IIRC) flatpak.