How to determine if the bootloader is locked The end point is for me to root my S6 but I figured I cannot do that if I first do not find out whether the boot-loader is locked or not although I am convinced it is unlocked. I need reassurance as I am not in the position to buy a new phone.

During my research I came across adb and fastboot, tools used by developers for Androids and adb does work but fastboot I cannot seem to get to work.

I tried rebooting to bootloader but it just loads the phone OS up straight away. Tried booting to ODIN MODE, tried booting to download mode, etc.

How can I find out if the bootloader is locked? My current approach is using fastboot and running the fastboot oem device-info command.
There's no fastboot for Samsung devices - Download mode is the semi-equivalent, except that it's only accessible via Odin/Heimdall. You will need appropriate drivers to get the PC to recognize a device in Download mode.

Most Samsung phones come with their BL unlocked or unlockable (notable exceptions are AT&amp;T/Verizon devices). To root these devices, turn on "OEM Unlocking" in Settings - Developer options (if the switch exists), find a custom recovery made for the device, and flash it with Odin/Heimdall, then finally flash SuperSU/Magisk. Alternatively, make a CF-Auto-Root package for your device and firmware version with firmware.mobi and flash it.