Hiding/Unhiding a slide in Keynote for iPadOS

I guess you mean skipping a slide during a presentation, i.e., the slide will be present, but will not be shown during the presentation. Here is how to do it in Keynote for iPadOS/iOS:

1. In the slide navigator: Tap the slide to select it, tap it again, then tap Skip Slide (or Unskip Slide to include it back again). You might need to tap ▶️, or rotate your device to see the Skip Slide/Unskip Slide command.

2. In the light table view: Tap to select a slide or select multiple slides, then tap the (the Skip button) or (the Unskip button) at the bottom of the screen.

_{The directions have been taken from the Apple Support pages for iOS and iPadOS}