What happened when you added the repo?
sudo add-apt-repository ppa:zorinos/stable
You can try in terminal:
sudo nano /etc/apt/sources.list
Then arrow key to the bottom and copy
deb https://packages.zorinos.com/stable focal main
and paste it at the bottom. Hit enter to drop down a line, then copy
deb https://packages.zorinos.com/apps focal main
and paste it in. Then hit ctrl+x to exit, the y key to say yes to save, then enter to save as current configuration. The terminal will revert to normal.
Enter in
sudo apt update
Then try installing the packages above, again.


