Torpor Orb reads: "Creatures entering the battlefield don't cause abilities to trigger." The key word is creatures. Under CR 603.6, triggered abilities that trigger when a permanent enters the battlefield are governed by the permanent's type at the time of the event. Planeswalkers are their own permanent type (CR 306.1) and are not creatures unless a separate effect makes them so.
Because a standard planeswalker is not a creature as it enters, Torpor Orb's replacement-style suppression simply does not apply to it. Any triggered ability the planeswalker has that says "when [this] enters the battlefield" will still trigger normally (CR 603.1).
If a planeswalker were also a creature — for example, if it had been turned into a creature by an effect like Oko, Thief of Crowns's +1 ability — then Torpor Orb would suppress its enter-the-battlefield triggers, because it would be entering as a creature (CR 603.6b).
Concrete example: You control Torpor Orb and your opponent plays Elspeth, Sun's Champion. Elspeth has no printed ETB triggered ability, but suppose a card with "whenever a planeswalker enters the battlefield, do X" exists — Torpor Orb would not stop that trigger, because Elspeth is a planeswalker, not a creature.
Bottom line: Torpor Orb is narrowly written to affect only creatures. Planeswalkers, enchantments, artifacts, and lands entering the battlefield are all unaffected by it unless they are also creatures at the moment they enter (CR 603.6, 306.1).
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.