Have you ran the
sudo apt update command? not
sudo apt-get update - for some reasons this makes a difference and it caused similar errors to me when I installed the OS on a laptop.
I’m not super tech-savvy either but maybe my advice will come in handy.
p.s. before you do so, can you check if you can run the
sudo apt-get upgrade command? In my case, I could not, before I ran the
sudo apt update command. Cheers.