From my experience this is suspect, the path to your bench is not correct - the problem may be with your install? bench.utils.CommandFailedError: npm install - #40 by clarkej
Another suggestion - with your listings, include the command prompt, so your audience will know the user account for example ‘frappe’ and the directory you run a command from for example ‘frappe-bench’
frappe@ubuntu1804lts:~/frappe-bench$ which bench
/home/frappe/.local/bin/bench
Also perhaps point to the ‘official’ install notes you used to perform the install.