Can you push someone upwards into the air?

I’m wonder about the pushing away keywording and if it’s valid to push creatures vertically. As an example lets check the monk ability.

Open Hand Technique

Starting when you choose this tradition at 3rd level, you can manipulate your enemy’s ki when you harness your own. Whenever you hit a creature with one of the attacks granted by your Flurry of Blows, you can impose one of the following effects on that target:

  • It must succeed on a Dexterity saving throw or be knocked prone.

  • It must make a Strength saving throw. Ir it fails, you can push it up to 15 feet away from you.

  • It can’t take reactions until the end of your next turn.

Q1: Can you use the second effect to push him away upward diagonal from you? if so, he takes 1d6 when falling to the ground and get prone?.

Q2: If some other mechanics claim push the creature X feet, can you push him those feet vertically? (like an uppercut kind of strike)