Here’s how to make a parallax slide transition from one slide to another. Strictly speaking, to fake it!
The parallax effect is created by making a text box ‘below’ the visible slide then animating that text box into view. See Cool Parallax Slide Transition in PowerPoint
Ideally, you’d be able to transition to the next slide rather than a text box. PowerPoint can’t handle that type of slide transition but it can be faked.
Make a second slide that you want to transition to.
Take a screen shot of the slide using the Insert | Images | Screenshot or other tool.
Then add the slide image to the hidden part of the parallax transition slide.
Make sure you add it to the existing Group (as listed in the Selection pane) so that the slide image is included in the animation.
Check the animation to ensure that it still works properly.
Finally, hide the second ‘source’ slide so it doesn’t appear in the presentation. Right-click on the slide thumbnail to choose ‘Hide Slide’.
This isn’t an ideal solution. The slide image might not scale properly on a larger display. Any change to the second slide means another screen shot and pasting into the main slide.