Here’s a gotcha if you’re installing Debian (or probably any other Linux based distro).

The installation iso already comes with a bunch of packages which you can use in the sources.list in the installed OS.

If I remember correctly, this is the default set-up, and one has to explicitly comment this out to use apt.

deb cdrom:[Debian GNU/Linux 12.2.0 _Bookworm_ - Official amd64 DVD Binary-1 with firmware 20231007-10:29]/ bookworm main non-free-firmware

Since my computer didn’t have a wireless network card, I could use a USB Wifi adapter and install some dependencies from here.