nvm is for installing node not npm, npm will be installed

What you're doing with nvm install npm, is attempting to install a node version called npm.

Do nvm install 14, let it run, check for errors, then once installed your have npm.

Generally speaking, loading arbitrary data from a URL into a root shell session is not a good idea and I wish people would stop peddling it as a solution for everything - "Please just run this script I'm sending you, and also while we're at it - I have a bridge you'd probably be interested in purchasing".

As an alternative, here's the "Ubuntu Way" of doing the same, where you can see how the system is being updated and know what repositories and what keys are added to your system configuration:

curl https://deb.nodesource.com/gpgkey/nodesource.gpg.key | sudo apt-key add -
sudo apt-add-repository "deb https://deb.nodesource.com/node_7.x $(lsb_release -sc) main"
sudo apt-get update
sudo apt-get install nodejs

And here's the "post deprecation of apt-key way" of doing the same thing:

curl https://deb.nodesource.com/gpgkey/nodesource.gpg.key | gpg --dearmor | sudo tee /etc/apt/keyrings/nodesource.gpg
echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_7.x $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/nodejs.list
sudo apt update
sudo apt install nodejs

This is for the latest (at time of writing) Nodejs version 7. Other versions can also be gotten with a simple change to the repo URL - consult nodesource.com documentation for details.

Node is one of the easier projects to build. Just change the version as that continues to change.

Browse to http://nodejs.org/dist/latest/ to find out the latest package version.

cd /usr/local/src
wget http://nodejs.org/dist/latest/node-v7.2.1.tar.gz
tar -xvzf node-v7.2.1.tar.gz
cd node-v7.2.1
./configure
make
sudo make install
which node

You should see /usr/local/bin/node.

Install nodejs v20 on Debian and Ubuntu based distributions

step 1 : Download and import the Nodesource GPG key

sudo apt-get update
sudo apt-get install -y ca-certificates curl gnupg
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg

step 2 : Create deb repository

NODE_MAJOR=20
echo "deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_$NODE_MAJOR.x nodistro main" | sudo tee /etc/apt/sources.list.d/nodesource.list

optional: here we are installing nodejs v20 but if you want to install v18 change NODE_MAJOR=18 in above command. Similarly if you want to install nodejs v16 then change NODE_MAJOR=16.

step 3 : Run Update and Install

sudo apt-get update
sudo apt-get install nodejs -y

congratulations you just installed nodejs

To uninstall nodejs

sudo apt-get purge nodejs &&\
rm -r /etc/apt/sources.list.d/nodesource.list &&\
rm -r /etc/apt/keyrings/nodesource.gpg