Yes, you can easily add a 3-column layout to your slide master in 8 steps:
1. Click the View tab. You see the View tab menu showing up.
2. Click the Slide Master icon in the Presentation Views group.
PowerPoint changes the presentation editing view to slide master editing view.
3. Click the Insert Layout icon in the Edit Master menu group.
You see a blank layout showing up.
4. Click the Insert Placeholder menu in the Master Layout menu group.
You see a list of placeholder types showing up.
5. Slect the Text placeholder. Then press donw the mouse button and
drag the mouse on the layout to insert a text placeholder to the layout.
6. Repeat the last step 3 times to add 3 text placeholders as 3 columns
on the layout.
7. Right-mouse-button click on the new layout icon in the left pane.
Then select the Rename Layout option, enter "Three Columns", and
click the "Rename" button. The layout will be renamed to "Three Columns"
8. Click the Close Master View icon in the Close menu group.
PowerPoint saves the new layout in the slide master and
changes to the presentation editing view.
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