Webinar issues

Welcome to the Zoom Community, @Legacy1.

Most likely you are sharing your screen or a window which also has your own Zoom windows on top of portions of your shared area. If you have dual monitors, move those Zoom windows to the other monitor. If not, go to your Settings -> Video window, scroll down and click the Advanced button, then try other options for Video Rendering Method and Video Capturing Method.  (These might be different on a Mac, this is a Windows PC screen shot)

Try this in a test meeting in advance, and figure out which settings eliminate the black boxes.

I haven't tested this extensively, but I know that these options do affect what layer of video is being grabbed, and whether the Zoom windows are being blacked out or shown in detail.