I have bench version 5.4.0(tired 5.3.0 as well). Also ERPNext is 12.16.2 and frappe is 12.13.0.
I had planned to update ERPNext from 12.16.2 to 12.20 which is the latest version in 12.
when i give the command bench update ,the update exits immediately.
No Error log is printed on the screen.
This is a new installation with data restored from an instance on another computer?
You could try: bench update --requirements, then bench migrate. Then try updating.
It may save time to revisit how the installation was performed on the machine in question, and see if there is some difference in the operating environment or source of the application that is the cause of the problem.