I do think you are on something here. I tried the install script earlier today. It detected that I ran node10 and let me choose what to do. I don't remember what the script said but I thought i've done correct. The script downloaded I believe 1,4Gb and needed a reboot. Therefore I thought thats done. What to do next?
When I try the script now it says:
Running Node-RED install for user pi at /home/pi on raspbian
Nodejs 10 is no longer supported.
You can update to the latest Node-RED 1.x version by adding --nodered-version="1.3.5"
to that install command. If in doubt this is the safer option.
Or you can force an install of node 12 or 14 by using the --node12, --node14 or --node16 parameter
However doing so may break some nodes that may need re-installing manually.
Generally it is recommended to upgrade all nodes to their latest versions before upgrading.
Please backup your installation and flows before upgrading.