A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Hello,
Welcome to Microsoft Community and thank you for posting your query.
I suggest you to try pressing **Ctrl + P (**short key for Pen) from keyboard in slideshow mode and check if you are able to use Pen. Also check if show pop-up toolbar option is enabled.
To do so, kindly follow the below mentioned steps and check if issue persist.
- Click or tap on File, then click on Options.
- Under Options, click on Advanced in left panel.
- Under Slideshow section, click on show pop-up toolbar checkbox to enable.
- Click on OK and check if it works.
I hope the above information helps. Let us know if you need further assistance.
Thank you.