Well, my raspberry pi came with a SD card that already contained some images. During the installation procedure, I chose to install LibreElec. The root of my SD card looks like: see attachment
Yes, that is NOOBS. If you press shift when booting, you can stop in NOOBS configuration. That includes a menu option to edit config.txt.
But if you only ever want to use LibreELEC then a fresh install of LibreELEC may be advisable - it saves some sdcard space and simplifies things like editing config.txt.