To widen columns in a column chart in Excel, follow these steps:

1. Click on the chart to select it.
2. Click on the column that you want to widen. This will select all the columns in the series.
3. Right-click on the selected columns and choose "Format Data Series" from the context menu.
4. In the Format Data Series pane, go to the "Series Options" tab.
5. Increase the "Gap Width" to reduce the gap between the columns. You can set it to a minimum value of 0% to have no gap between the columns.
6. Increase the "Series Width" to widen the columns. You can set it to a maximum value of 500% to make the columns very wide.
7. Click "Close" to apply the changes.

If you have already set the x-axis to category, then widening the columns should work. However, if the chart was copied from PowerPoint, it may have some formatting that is preventing you from making changes. In that case, you can try copying the chart to a new Excel workbook and then making the changes.