How should the "and/or" text of a card be interpreted?
You must choose X different[1] targets, and the targets can be creatures and/or planeswalkers. With X=2,


You can target two different creatures,
You can target two different planeswalkers, or
You can target a creature and a different permanent that's a planeswalker.


This is confirmed by a ruling for Pinnacle of Rage: "You must choose two legal targets to cast Pinnacle of Rage." (The ruling dates back to when Pinnacle of Rage still used the same wording about which you are asking.)



Notes:



  114.3. The same target can’t be chosen multiple times for any one instance of the word “target” on a spell or ability. [...]