Weather Icons Broken OpenWeather Gnome Extension
Solution 1:
I had the same problem with Ubuntu 20.04 and the Adwaita (default) icon set.
I could fix it by selecting another icon set like Paper.
You can switch the icon set with Gnome Tweak Tool. Install that using sudo apt install gnome-tweaks.
Solution 2:
I changed the icon set to Adwaita++, you can download it here. They have install instructions.