There’s a bad bug in the latest Keynote update for iPadOS (and probably iOS, too). If, on first launch, you open a presentation with font warnings, after dismissing the font warning box you’ll be presented with a totally unresponsive Keynote. You have to open a presentation with no font warnings (or start a new one) in order to get Keynote to get going, which I accomplished through the Haptic Touch context menu. Once that’s done, you are prompted with the “what’s new in Keynote” modal…which likely was the culprit for the whole thing. Ugh.