Ubuntu 18.04 wont open terminal after Python 3.7.4 install

You have two Python version installed.

sudo gedit /usr/bin/gnome-terminal

Edit #! /usr/bin/python3 to #! /usr/bin/python3.6

Maybe go to sudo update-alternatives --config python3 and set the Python 3.6 as default, or you may found problems with add ppas's, commands not found etc.