Microsofthuyen137 I think the issue may be that you get to PowerPoint Live and Whiteboard as the initial selection of what you want to share. You do not open them as you are sharing a screen or window. What I mean is that if you want to present a PowerPoint Live - when you go to initiate the share, you do not select a screen or window... instead - if you look down you will see Microsoft Whiteboard and then lower you will see PowerPoint Live. If you have recently opened the PowerPoint, it may be listed in the files under PowerPoint Live. If so, select it and you are off and running. If not, then select the Browse OneDrive or my computer to find the file and select it. If you select Microsoft Whiteboard - it will open the whiteboard associated to the meeting you are in. If you want to share a different one, you will need to share your screen and then open that other whiteboard to share it.
I hope this helps!
