Formatting error: preventing line breaks in words

Keynote is not a word-processing application and you have very limited control over how text flows in the Text box. You can manipulate the text box width, the font and its attributes, its character spacing, or justification.

Here is the same text from Keynote v14.3 on Sequoia v15.3.1 that is justified in 21 pt Helvetica:

You may be able to tighten the selected text further using a negative character spacing on the Options panel:

I also can't replicate this. I retyped your text, but no matter what text styles I set, I can't get it to break a word. Full justification just adjusts the spacing between words to fit the margins.

So it makes me wonder if there's some underlying attribute to the text that we're not seeing.

Where did the text come from? Did you type it directly in Keynote? Copy it from some other application? The fact you mention a 'HTML cleaner' implies that it's coming from somewhere else.

The text was processed with an "HTML format cleaner" before pasting into the Keynote text box per the OP.

You can use live text directly on the OP's image in the browser to select text and then paste into Keynote. It does require some cleanup though.

That's my point, though. Where did the OP's original text come from?

Typing the text directly into a text box doesn't exhibit the behavior (that I can replicate, at least).

Also relevant is whether the line breaks are embedded in the text, in which case resizing the text frame won't make a difference.

Agreed.