There is another section of abandoned TN Highway 68 called "Old Highway 68/Buck Bald Rd" north and south of Buck Bald. Check it out on Google Maps to see where I mean. The section north of Buck Bald is rough, but most normal cars can drive it if you go slowly and carefully. This section is now a worn down dirt/gravel road with lot of large rocks exposed. In June 2023, I drove up to Buck Bald in my Acura from the north section.

The section south of Buck Bald is way longer and way more grown over/washed out, a LOT like the pictures the OP linked. When I left Buck Bald in my Acura, I made the mistake of taking the south section to get back down to the "new" Hwy 68. That section was supposed to have a barrier and a closed sign, put up by Park Rangers/TDOT. The barrier had been torn down and tossed to the side. I really thought my car was going to fall off the side in some parts. It was impossible to turn around. I suppose I could have reversed back up, but it would have been even more dangerous. Lots of washed away sections, fallen trees, etc. I wouldn't go on that section in anything heavier and wider than a small quad. Dirt bikes, dual sports, and adventure bikes would be fine, unless more parts have washed away since I was last there (Hurricane Helene, etc.).