Admittedly, those instructions need to be read in a spiral.Where exactly did you see that? I must have missed it. The instructions are somewhat confusing for someone like me who doesn't know what category a particular device falls under.
This is what I've done:
- Flash latest firmware. Force reboot to download mode.
- Flash TWRP in AP using Odin. Force boot to recovery (hold volume up) to boot into TWRP.
- Wipe data. Flash multidisabler. Command reboot to recovery via TWRP reboot menu.
- Flash Magisk in TWRP. Reboot to system.
- Have rooted device.
I just looked at them again and do not see what I remembered: they say "will reboot automatically", I remember something saying it's important to make sure go from Odin to recovery with no intervening boot of Android (regular Android, not the stripped down thing they use for recovery).
From your description, what you did is what I thought it should be, as long as we equate TWRP with recovery.
Now, if @HyruleanKnight can reproduce your steps...