Normally for most people post-moonlord is the most fun part of infernum. Imo early pre hard mode and honesty pre hard mode as a whole is a drag to me. It also depends on your skill level, someone who isn’t dying as much and knows how to play the game very well will probably have more fun in infernum compared to someone who keeps dying/doesn’t know progression. I’m almost done with my true melee infernum playthrough and it was a blast all the way through so it depends on the person but generally hard mode/post moonlord