Does the Horizon Walker ranger's Planar Warrior feature bypass resistance to non-magical attacks?

Question

The Horizon Walker ranger's Planar Warrior feature (XGtE, p. 42-43) says:

As a bonus action, choose one creature you can see within 30 feet of you. The next time you hit that creature on this turn with a weapon attack, all damage dealt by the attack becomes force damage, and the creature takes an extra 1d8 force damage from the attack. When you reach 11th level in this class, the extra damage increases to 2d8.

Some creatures have:

Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks

Does the Planar Warrior feature bypass that resistance, since even if the attack is made from a normal weapon, the damage is changed into force damage?

Answer 1

Yes, the attack would bypass that reistance

Creatures that say this only resist B-P-S damage types

Damage Resistances bludgeoning, piercing, slashing from nonmagical attacks

When a statblock says this, it means that the creature only is resistant to the bludgeoning, piercing, and slashing damage types from nonmagical attacks. Since force damage is its own damage type, it ignores this statement completely and affects the creature like normal (no resistance).

The next time you hit that creature on this turn with a weapon attack, all damage dealt by the attack becomes force damage

The fact that this ability changes all damage to the force type before damage is inflicted means that the weapon doesn't matter here, it just counts as force damage no matter what.

The force damage would bypass the resistance even without the B-P-S phrase

In the Basic Rules in the section detailing the different damage types, force damage is described as follows:

Force. Force is pure magical energy focused into a damaging form. Most effects that deal force damage are spells, including magic missile and spiritual weapon.

Which means that any force damage should be automatically considered to be magical regardless of the source. See Does Force damage count as magical if the feature causing it doesn't? for more discussion on that case.

Thus, even a creature resistant to all non-magical attacks would still not be resistant to the Planar Warrior's attack.

Answer 2

Yes

The resistance is to those specific damage types - bludgeoning, piercing and slashing. Planar warrior changes all of the damage to force damage so the damage resistances don't apply unless they also had force damage resistance.

Damage resistances are only applied when you are actually applying the damage to the creature. It doesn't matter that the damage would normally have been B,P or S, it only matters that the damage is now force damage.