Hello @penflame, Welcome to the /e/ forum.
to instal Custom Android on a Samsung device you first need a Custom Recovery manager like TWRP.
Searching for android_device_samsung_r0s source,
i found TWRP for (r0s) with install instructions here :
https://github.com/afaneh92/android_device_samsung_r0s/
.
Also,
fastboot command is expected not to work on Samsung device
you need to use
- Odin3 Windows GUI
- or Odin4 Linux CLI (that can be managed by Galaxy-Flasher GUI)
- or Heimdall 2.1.0 Linux CLI
- or Heimdall-frontend 2.1.0 Linux GUI
- or Eros Android OTG GUI
to install the Custom Recovery,
.
then with the device booted in recovery mode,
you should be abble to install /e/ GSI :