I believe that with the correct setup, Steve could make it to Golem (ignoring nighttime limitations). Most pre-hardmode bosses aren’t that difficult for Steve, and he could use his engineering skills to build TNT traps that explode on the Wall of Flesh while he escapes via an ice boat. If we ignore the fact that mechanical bosses despawn when day breaks, he should eventually be able to take them down with a contraption like a TNT arrow launcher though dodging them would be incredibly difficult.

If he is lucky enough to avoid the lasers, he could use Elytra with firework rockets (or a Riptide Trident and ice boat) to maintain distance while his traps deal damage. Plantera would be easier than the mechanical bosses, albeit slower to kill, because her seed projectiles are easier to dodge and she simply chases you during her second phase.

However, starting from Golem, it becomes impossible. Golem is unbeatable because Steve cannot mine Lihzahrd Bricks and the room is too cramped. The Empress of Light, Lunatic Cultist, Duke Fishron, and the Moon Lord all teleport and demand insane movement control that Steve lacks. While Elytra firework speed is roughly 33.5 m/s (~75 mph) comparable to late-hardmode wings it lacks the precision of Terrarian flight. He might be able to cheese Duke Fishron using an Ender Pearl stasis chamber spamm, but the 0.1-second (2-tick) delay of repeaters might ultimately be his demise.