Add bold, italic, underline, or strikethrough to text in Keynote on Mac

select text you want to change.
To change all of the text in a text box or table cell, select the text box or table cell.
In the Format sidebar, click the Text tab, then click the Style button near the top of the sidebar.
Click one or more format buttons in the Font section.
To remove a specific format, click that button again.
If the font you’re using has other styles available (such as light or condensed), click the pop-up menu above the buttons to choose one of them.

Tip: You can set keyboard shortcuts to quickly apply bold, italic, underline, or other character styles to text.

Helpful?

Keynote User Guide for Mac