After you are in a Zoom meeting:

Start PowerPoint

Open Presentation

Click SLIDE SHOW menu item

Click FROM BEGINNING ribbon item

ALT-TAB back to Zoom window

Click SHARE SCREEN button in Zoom

Select SLIDE SHOW Screen from available share items

If you have audio, check SHARE COMPUTER SOUND box

Click blue SHARE Button when time to share

Advance slides with click, spacebar or arrow keys

At end STOP SHARE SCREEN (Host may do this for you)