Can cards that say "deal damage to any target" deal damage to a planeswalker?
Yes, any target includes planewalkers

The wording was a relatively recent change. Previously, very few damage-dealing spells and abilities could target planeswalkers directly. Instead, you redirected damage from targeted players to one of their planeswalkers at resolution.


  114.4. Some spells and abilities that refer to damage require “any target,” “another target,” “two targets,” or similar rather than “target [something].” These targets may be creatures, players, or planeswalkers. Other game objects, such as noncreature artifacts or spells, can’t be chosen.