If your have installed nodered earlier, but through the "vendor supplied script", you've noticed that the installer chokes on nodered. You'll also see that both nodejs and npm that are found on your system are my=uch higer than required.
In essence, the script adds some repositories to apt that include "non-official packages"...
Although installer.py is purely meant to run on a freshly installed raspbian, we've noticed that many people try to run it on "more customised systems". For the installer (install.py) to work properly, you have to remove these packages and remove the "non-official repositories.
Please note: this procedure is tested, but without any warranty!!!!!
This is how you can get rid of the "non offical packages":
sudo mv /etc/apt/sources.list.d/nodesource.list ~ sudo touch /etc/apt/sources.list.d/nodesource.list sudo apt update sudo apt remove nodejs sudo apt remove npm sudo apt purge npm sudo apt remove npm/stable sudo apt purge npm/stable sudo apt update sudo apt install nodejs sudo apt install npm sudo apt remove nodered sudo apt purge nodered
That should do it, you now have the correct version of the required packages AND you can now install nodered through the installer (install.py). I need to check the autostartup of the older nodered, bt this is a good start.