If OneNote is not allowing you to format text in multiple columns, one possible cause could be that your document was originally authored made up of multiple tables with a single column.

If this is the case, then follow these steps in order to set up a multi-column layout in OneNote:

1. Highlight the section of text to be formatted.
2. Click on the Table tool in the ribbon.
3. Select Insert.
4. From the drop-down menu, select Convert to Text.
5. Highlight the converted table of text.
6. Choose the column and row layout you need.