Keynote 14.4 shows spinning beach ball in Tahore 26.2

'when using..."

When opening the application?

When opening a specific document?

When adding slides?

When adding content to a slide?

During presenting?

There isn't enough information in your post to be able to determine a cause, or a solution... at least beyond stabbing in the dark.

Please provide more information.

There are too many variables, and not enough information to be able to answer this.

First is whether the presentation itself is large and complex, or simple - does this happen on a new, basic presentation with just a few slides?

Second it what else is going on with the machine at the time? Is Keynote the only major app open, or are you running Mail, Photoshop, Final Cut Pro and Excel in the background, while listening to your favorite podcast as you work?

What does Activity Monitor.app have to say? it might indicate CPU or memory pressure, along with likely candidates.

Without more information to go on, there's not much more that I can add.