You don't say what OS you are using, but the sources for Raspbian Buster should be something like:-

deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi

Restoring it should be OK.

NOTE 1 I NEVER use sudo nano - you should use sudoedit which edits a temporary file.

NOTE 2 raspbian.raspberrypi.org is slow and unreliable. I replace with a local mirror; in my case deb http://raspbian.melbourneitmirror.net/raspbian/ buster main contrib non-free rpi although you could select a local mirror from https://www.raspbian.org/RaspbianMirrors/

NOTE 3 I rarely edit /etc/apt/sources.list.d, but add additional repositories to /etc/apt/sources.list.d I have /etc/apt/sources.list.d/vivaldi.list among others.

NOTE 4 I don't know who suggested using a Ubuntu build; it may or may not work; it is safer to build from source.

You don't say what OS you are using, but the sources for Raspbian Buster should be something like:-

deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi

Restoring it should be OK.

NOTE 1 I NEVER use sudo nano - you should use sudoedit which edits a temporary file.

NOTE 2 raspbian.raspberrypi.org is slow and unreliable. I replace with a local mirror; in my case deb http://raspbian.melbourneitmirror.net/raspbian/ buster main contrib non-free rpi although you could select a local mirror from https://www.raspbian.org/RaspbianMirrors/

NOTE 3 I rarely edit /etc/apt/sources.list, but add additional repositories to /etc/apt/sources.list.d I have /etc/apt/sources.list.d/vivaldi.list among others.

NOTE 4 I don't know who suggested using a Ubuntu build; it may or may not work; it is safer to build from source.

You don't say what OS you are using, but the sources for Raspbian Buster should be something like:-

deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi

Restoring it should be OK.

NOTE 1 I NEVER use sudo nano - you should use sudoedit which edits a temporary file.

NOTE 2 raspbian.raspberrypi.org is slow and unreliable. I replace with a local mirror; in my case deb http://raspbian.melbourneitmirror.net/raspbian/ buster main contrib non-free rpi althogh you could select a local mirror from https://www.raspbian.org/RaspbianMirrors/

You don't say what OS you are using, but the sources for Raspbian Buster should be something like:-

deb http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://raspbian.raspberrypi.org/raspbian/ buster main contrib non-free rpi

Restoring it should be OK.

NOTE 1 I NEVER use sudo nano - you should use sudoedit which edits a temporary file.

NOTE 2 raspbian.raspberrypi.org is slow and unreliable. I replace with a local mirror; in my case deb http://raspbian.melbourneitmirror.net/raspbian/ buster main contrib non-free rpi although you could select a local mirror from https://www.raspbian.org/RaspbianMirrors/

NOTE 3 I rarely edit /etc/apt/sources.list.d, but add additional repositories to /etc/apt/sources.list.d I have /etc/apt/sources.list.d/vivaldi.list among others.

NOTE 4 I don't know who suggested using a Ubuntu build; it may or may not work; it is safer to build from source.