Sharing PPT

hooperm Hello Mandy, it's the most recently used documents that are available when you click the "Share" button. In other words, if you're updating and/or fine tuning your presentation it's going to sit right there for you (note SharePoint/OneDrive).

Here's the official documentation 

"The PowerPoint section lists the most recent files you've opened or edited in your team SharePoint site or your OneDrive. If you select one of these files to present, all meeting participants will be able to view the slides during the meeting. Their access permissions to the file outside of the meeting won't change.

If you select Browse and choose to present a PowerPoint file that hasn't been uploaded to Teams before, it will get uploaded as part of the meeting. If you're presenting in a channel meeting, the file is uploaded to the Files tab in the channel, where all team members will have access to it. If you're presenting in a private meeting, the file is uploaded to your OneDrive, where only the meeting participants will be able to access it."

https://support.office.com/en-us/article/share-content-in-a-meeting-in-teams-fcc2bf59-aecd-4481-8f99-ce55dd836ce8