This is what I see:

Maybe I should add some files to some directory. I'm extremely new to ubuntu so please give a detailed solution.
21 Answer
Here you have two problems with repositories - they do not have packages for Ubuntu 20.04 LTS.
So you need to remove these repositories at first with
sudo add-apt-repository -r ppa:danielrichter2007/grub-customizer sudo add-apt-repository -r ppa:ppsspp/stable and then add repository which provides ppsspp package:
sudo add-apt-repository ppa:samoilov-lex/retrogames sudo apt-get update sudo apt-get install ppsspp