The Rescuers Down Under (1990) was the first feature film to be 100% recorded to film from digital files. BATB, Aladdin, Lion King, Toy Story were also all done entirely digitally as were other animated films put out during that time.
I’m pretty sure they used a DI for the Phantom Menace, that pre-dates O Brother Where Art Thou by 1 year for a live-action movie.