It cannot do two things at once. To prevent chaos, it creates a "lock file" whenever it is working. Think of this like a "Do Not Disturb" sign on a hotel room door.
Once done, you can proceed with your original install command. It cannot do two things at once
This fixes any remaining broken dependencies. It cannot do two things at once
To understand the error, you have to understand how Linux package management works. It cannot do two things at once
— it’s a common issue, and easy to fix.
sudo apt update --fix-missing sudo apt install -f