If you only have one screen, you can still share your PowerPoint slides without showing the thumbnail view,.

Don't show your thumbnails!
Method 1: Alt + tab method to select your Zoom window (or PowerPoint window)
Method 2: Show the presentation in a window. In PowerPoint, select the slide show tab, then "Set Up Slide Show" then select the 2nd button "Browsed by an Individual (window). You can resize the window