There are some Scandinavian designs that cover the entire knife, and one of them has a thong threaded through it for neck carry. If I can find a picture I'll post it here.
Edit: Found one, the link goes to pintrest where there are more images like this one.
https://images.app.goo.gl/1KumawYQJBHbQ8mN8
The old Buck 105 sheath, and the DPx HEFT4 sheaths folded over to cover the handle. I don't even like keeper straps, though; so I wasn't a fan of those knives for carry. Great for just dropping a knife in a pack, though.
I don't know if any for knives that would be suitable for neck carry...wouldn't that feature be self defeating?