The latest version of pip does not support Python 2.7, which has been at end-of-life for a year now. Instead, you’ll need to use the last version of pip that did support Python 2.7; you can use https://bootstrap.pypa.io/2.7/get-pip.py to get it.
But if at all possible, you’ll be better off upgrading to Python 3.8 or newer
Ubuntu 20.04 ships with Python 3.8 by default. You can run it with the python3 command. Some tutorials might say to run python ... but just run python3 ... instead.