Hello folks. Below is a text version of the solution as well as a timestamped video for all 5 Achievements in Title Update 3.
For Secret Crystal 5, we need to play Level 15. Levels unlock as you play the game, so you'll need to get through the previous levels to get here.
When you start, you'll see the crystal to your left. Go to the right of the box nearby and push it left, in the first hole that leads to the crystal. Now go right, passing a single set of trapdoors and continuing beyond the red/blue button. Cross another trapdoor section to find a box up top. We need to push the box back across the previous trap door sections to place it so we can reach the crystal, so time your pushes carefully. Once you're dropped the box in the other hole, walk across the boxes to get Secret Crystal 5.
Level 15 starts at 3:31