@sf98723 - https://developer.apple.com/forums/profile/sf98723 Hi. Thanks a ton for this help. Installed Big Sur thinking that deleting the problematic AppleThunderboltNHI.kext would be no prob but of course having issues. BTW can you explain your steps in a bit more detail? I'm going to be essentially copying and pasting your recommendations so hopefully everything you shared will work. I have no clue what mount -uw will do if I wrote this wrong. Also what should I be putting in when you state <your custom stuff>? What should we be beware of, so we don't do something really disastrous accidentally  Thank you!

@sf98723 Bonjour! Thank you for the clarification. Unfortunately I'm now stuck on restart loop. I'm getting error "Your computer restarted because of a problem. Press a key or wait a few seconds to continue starting up." Not sure what I did wrong. Was I supposed to do step 8 after one more reboot? I did steps 8 & 9 immediately after step 7. Luckily, I can enter recovery mode, but cannot enter normal mode. Shall I reinstall Big Sur again and repeat your steps one more time? Any recommendations? I'm also on MBP mid 2014. I upgraded from Catalina. Had been removing ThunderboltNHI kext since the issue popped up the last couple of months. Yours, from Mongolia! UPDATE: I disabled csrutil and then - Voila! restarted just fine! And the problem child driver is gone! Wow. UPDATE 2: It seems now my MBP goes into restart loop if I enable <<csrutil authenticated-root>>. Any recommendations? MBP seems to be working fine otherwise (no security but at least working 😂)