Did you manually install nodejs version 15.9? That is not a supported version, though it does not mean that that is the problem. To rule it out, however, I would start by removing nodejs and then re-running the script, which will install a supported version. You should be able to remove nodejs by doing
apt remove nodejs
If it still doesn't work then post install log here (it tells you where it is at the end of the script). The log may have multiple runs of the script there so just post the last one.
See this post for details of the best way of posting logs and flows - How to share code or flow json
