where has my sources.list gone?

[Milehighyena]

I have build a retropie inside of an NES cart using a 16gb image from 2017 onto a pi zero. I would like to add some C64 games and DOS games to it. When I tried, it told me that I need to upgrade from Raspian stretch to buster. So I set to learn the steps to do that. However, I get as far as updating the apt packages in the /ect/apt/sources and my pi tells me that the ect/apt and even the /ect file is missing.

I'm still very new to using linux in general, and my research into this problem isn't helping me. I would like to know how I can create an /ect/ file and i suppose also an/apt file where I can place the deb packages addresses for debian Buster. or do the thing where I replace the Stretch in those files to Buster. But first, I need to put my /ect/ file back in there. How?

[mitu]

Upgrading the OS is not supported by Raspbian nor RetroPie. You probably have found some instructions on how to upgrade using apt and updating its configuration files in /etc/apt, but it's not a recommended process, especially for a beginner.

If you wish to use an up-to-date/current version, use the image from http://retropie.org.uk/download. We don't support 3rd party image, as outlined in https://retropie.org.uk/forum/topic/3/read-this-first.