will try that later when back at the notebook. When I install your last software recommendation, how do the system / or I select WHICH software is responsible for installing at the end? Don‘t they conflicts each other?
You can right click and choose which installation app to use. Or, right click and select the properties, then the "open with" tab. At the lower right you can see a button to set your selection as default.
They won't. Gdebi is its own software and does not rely on the Gnome-Software application at all.
Don't worry. This is an easy thing to fix once you have encountered it more than the very first time.
Elevate your terminal to root by:
Now, launch your file manager from within that elevated terminal to elevate your file manager to root:
Tap "Other locations" in the left pane. Then "Computer" in the right pane.
You are Now In Root.
You should see the directory for etc
Open it, then go to apt then Right Click on sources.list and choose Open With > Text editor
With it open in the Gedit text editor, tap ctrl+F for the Find function.
Paste in deb http://repository.spotify.com
Or just spotify
Find the line that added deb http://repository.spotify.com to the list and remove that one entire line for Spotify.
Save the file.
Open a New terminal window and test that all is well with:
sudo apt update
If all is well, close the text editor, elevated Nautilus File Manager and the Elevated terminal.
It sounds like the line curl -sS https://download.spotify.com/debian/pubkey_0D811D58.gpg | sudo apt-key add -
blended in with echo "deb http://repository.spotify.com stable non-free" | sudo tee /etc/apt/sources.list.d/spotify.list
In other words, both separate commands were put into the terminal as one command. They must be separate:
To add the repo KEY, paste in: curl -sS https://download.spotify.com/debian/pubkey_0D811D58.gpg | sudo apt-key add -
Tap the enter key. Once done, add the repository: echo "deb http://repository.spotify.com stable non-free" | sudo tee /etc/apt/sources.list.d/spotify.list
Then tap enter.
@Aravisian I thank you very much for your kind and honest support. I now was able to run thru all of your commands and installed everything and the native spotify client. As far as I can see for now, no other errors popped up since then.
One little difference occured while copying the given commands from you: The pubkey you gave run into an error but I interchanged it with the one from the spotify page and then everything was fine.
That was my first operation at the open heart of that new and for me unknown operating system and again, I can't thank you enough not only for helping me to solve the problem but more to get in deeper touch with this uncharted territory...