Hi everyone,
I’m a complete beginner, but I really want to build myself a Smart Mirror.
Unfortunately I’m already failing at the installation and I hope that you can help me so that I can get it up and running at some point. I’ve already tried several times, but it just won’t work.

I have got a Raspi 3 with Raspberry Pi OS (Legacy) Full

What have i done:
i took the installation tutorial from
https://docs.magicmirror.builders/getting-started/installation.html#manual-installation

but first i took the update by sudo apt-get update

Than installed node.js by sudo apt-get install -y ca-certificates curl gnupg

and
sudo mkdir -p /etc/apt/keyring

curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg

and updated again.
Everything fine and i got node Version V12.22.12

so i started

git clone https://github.com/MichMich/MagicMirror

got following informations in my terminal

Klone nach ‘MagicMirror’ …
remote: Enumerating objects: 25814, done.
remote: Counting objects: 100% (172/172), done.
remote: Compressing objects: 100% (94/94), done.
remote: Total 25814 (delta 79), reused 137 (delta 63), pack-reused 25642
Empfange Objekte: 100% (25814/25814), 21.49 MiB | 4.92 MiB/s, fertig.
Löse Unterschiede auf: 100% (15969/15969), fertig.

go to
raspberrypi:~ $ cd MagicMirror/
raspberrypi:~/MagicMirror $

npm run install-mm

But than every time i got following Info:

bash: npm: Kommando nicht gefunden.

What am i doing wrong???

I tried it one times more. Than changed the folder to MAgicMirror Old to start following

bash -c  "$(curl -sL https://raw.githubusercontent.com/sdetweil/MagicMirror_scripts/master/raspberry.sh)"

I would really appreciate any help! :-)
Greetings
Sven