It works for the latest Big Sur release 11.4. Follow the steps and post the steps and detailed difficulties you encounter

Back to this forum after a few monthes, sorry. Check in rescue mode the authenticated-root setting is disabled. Otherwise : infinite loop with kernel crash

Check «  csrutil authenticated-root status » in rescue mode. Sometimes it falls back to « enabled » but it MUST be disabled (seal broken by the fix) three days ago I went to an Apple store for a battery replacement for my MacBook Pro 15’ mid 2014 : the automatic diags reset this setting to « enabled » 🙌 (and Apple does not provide any battery replacement for this device although they publish the price for this replacement on their support web site 🙌🙌) in French : j’ai particulièrement soigné leur survey avec une jolie note de satisfaction. Le gars m’a pris de haut quand je lui ai expliqué le pb hardware de ces mac, il s’est retrouvé face au redémarrage en infinite loop. Je l’ai regardé avec compassion et je me suis barré je remplacerai la batterie avec celle que vend ifixit 😁😁

try mount -uw "/Volumes/Macintosh HD' or mount -uw /Volumes/Macintosh\ HD...

Just reinstalled a fresh 11.4 Big Sur on the same Mac. Obviously, authenticated-root has been reenable after the steps I’ve provided above. If your Mac loops at boot after these steps (kernel crash), do not forget to reboot in rescue mode and check csrutil status and csrutil authenticated-root status, in order to check that csrutil is enabled and authenticated-root is actually DISABLED. these steps already work like a charmed with Big Sur 11.4 ! otherwise I’ve not the tools to replace the faulty FDMF6808 chips … as Big Sur will be the latest os for my MacBook, it should live a long time without using the thunderbolt host interface

Google it. Try quotes and do not let trailing slash. Let me know