App “Software & Updates” not responding

I am on Ubuntu 20.04 and I experienced this problem. I tried the posts that recommended reinstalling python3-six and python3-certifi, but those didn't work for me. However, software-properties-gtk did start working again for me after I reinstalled python3-requests and python3-idna. So, to sum up the commands I ran:

sudo apt install --reinstall python3-six python3-certifi python3-requests python3-idna
sudo apt install --reinstall software-properties-gtk
software-properties-gtk

and I was back in business.

Same problem on Ubuntu 20.10... I had a look to dbus messages:

sudo systemctl status dbus.service

and saw this line:

.../... com.ubuntu.SoftwareProperties[8310]: ModuleNotFoundError: No module named 'chardet'

So I reinstalled chardet:

sudo apt install --reinstall python3-chardet

and software-properties-gtk is back.

The log shows:

dbus-daemon[1130]: [system] Successfully activated service 'com.ubuntu.SoftwareProperties'

Hope it helps.