Thanks for clarifying what you are trying to do. This is my workaround for a lack of a dedicated text wrap tool, its based on a Photoshop technique for masking:
Text wrap in Keynote
1 - place a rectangle shape on the slide and size it appropriately to hold the text
2 - place the image file on the slide and position it where required:

3 - add a second rectangle shape and size and position it exactly on top of the image
4 - select both shapes using; shift click
5 - Format > Shapes and Lines > Subtract
a hole is cut on the first shape to create a mask, revealing the image:

6 - double click on the large shape to select the text tool, then type or paste in text on to the shape
7 - format the text and colour the shape:

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