If yarl isn't installed, it should show different error message. Trying to upgrade or reinstall is better option
I see OP use python 3.6 where yarl isn't released yet,
yarl has no Python 3.6 builds. Because that I suggest to
pip install yarl, IMO.
on electrum website had noted - Python (3.6.1 and higher)
According to
https://pypi.org/project/yarl/,
yarl is available for Python 3.6
I had also downloaded the Appimage. But when I clicked on it, nothing happened, nothing at all.
You either haven't set AppImage as executable or it's quit as soon as you open it (hence it looks like nothing happened). Try to run AppImage from terminal and see any errors
cd /path/to/where/appimage/is/located
./electrum-4.0.3-x86_64.AppImage
Any one of those commands gives this:
Command 'pip' not found, but can be installed with:
sudo apt install python-pip
Attempting this, I get what's coming below (sorry, I don't know how to make it shorter). None of it I am able to understand, except of course the 404's which I wouldn't know how to get around.
Most likely there's problem with your internet, unless you attempt to configure network setting on Ubuntu by yourself.