...
Open the desired PowerPoint presentation
Select the Slide Show tab
Click Set Up Slide Show
Select Browsed by an individual (window)
Click OK and start slide show
Resize the window as need needed so you can see both Juno session and slides
...
Open the desired Keynote presentation
In the File bar, click Play
From the dropdown, click Play Slideshow in Window
Begin sharing your screen in Juno
...
Setup Google Slides for Screen Sharing
Open the desired Google Slides presentation
Click the Present button
Hover over the bottom-left of the slide
Click the three vertical dot icon
Click Exit full screen
Resize the window as needed so you can see both Juno session and slides