Making a digital copy of a physical book is fair use under every legal structure I am aware of.
When you do it for a transformative purpose (turning it into an LLM model) it's certainly fair use.
But more importantly, it's ethical to do so, as the agreement you've made with the person you've purchased the book from included permission to do exactly that.
Per the ruling, the problem is the books were not purchased, they were downloaded from black market websites. It's akin to shoplifting, what you do later with the goods is a different matter.
Reasonable minds could debate the ethics of how the material was used, this ruling judged the usage was legal and fair use. The only problem is the material was in effect stolen.
When you do it for a transformative purpose (turning it into an LLM model) it's certainly fair use.
But more importantly, it's ethical to do so, as the agreement you've made with the person you've purchased the book from included permission to do exactly that.