I don’t know how many times I have asked for this page to be modified as Unsuitable for Samsung.
Samsung uses Odin mode in place of fastboot. So fastboot will always fail in an Odin equipped Samsung. The issue is briefly mentioned as a footnote to this page Know your hardware - Samsung.
You can and should use heimdall to install either /e/ Recovery or TWRP as your recovery as described in the install instructions you quoted. /e/ Recovery is a “simplified” custom recovery while TWRP is custom recovery often preferred by experts.
If one is using /e/ Recovery one would omit the “navigation” instruction
- In TWRP return to main menu, then tap Wipe
but look for and find Format Data within the /e/ Recovery menu:
- Now tap
Format Dataand continue with the formatting process.