Hi Vicky,
When we tried to replicate the concern on our end using the PowerPoint Version 1910 (Build 12130.20344), it seems that we are unable to get the same results as yours.
Could you please provide us which build and version of Office you are using? To get this information, you may follow the steps on this link.
Also, kindly provide us the specifications of your device together with the build and version of Windows you are using. To get this, click the Start menu and type
About your PC and then select the first results. For build and version of the Windows, click the Start menu and type
winver and then hit Enter.
A video of the specific concern is another way for us to have a better overview of the exact issue. This way, we'll be able to capture how you annotate using the pen in the PowerPoint. Also, it can help us easily follow on how you do it if we
need to reproduce the problem on our end. We suggest that you save the video on your OneDrive and share the link with us by replying to the private message that we’ve sent to you together with the needed information above. Here's the articlefor
your reference. To get into your inbox, click your profile name on this thread and then select View private messages.
For any results, please let us know by replying to this thread, and we will get back to you as soon as we can if further assistance is needed.