Google Meet provides an integration with Google Slides which allows you to control your presentation directly from a Google Meet window.  Presentations created in Google Slides, as well as simple PowerPoint files without complex formatting or animations can also be uploaded to your Google Drive and used with this integration.  Complex PowerPoint files may have distorted formatting when viewed in Slides, and may need to be viewed as a screen share.

Getting your Presentation into Google Slides

First, get your presentation into Google Slides.  If you created it in Google Slides, you can skip the rest of this step.

If you have a simple PowerPoint file, upload it to your Google Drive.  Go to Google drive and click the New button.

Then choose File Upload.

Your file will be added to Drive.

Presenting in Meet

First, start your meeting. While your meeting is running, open a new browser tab, return to your Google Drive and double-click on the presentation.

In the presentation click on the Meet icon, then "Just Present this Tab".

Click your browser's Allow button on the screen that pops up. 

Return to the tab that you're using for meet and the presentation will be visible.  You can advance your slides with the controls at the bottom.

If you want to see speaker notes, click the three dots next to the presentation controls and choose Show Speaker Notes.  Only you will see the speaker notes.

When you're done with your slide show, click Stop Presenting at the top of the Meet window.