The visual picture is removed on many browsers in Zoom and other conferencing tools due to the security levels of DRM - Digital Right Management, including Safari and Chrome.
You may find your playback of the file to be a black screen with your watermark similar to the image below.
To resolve this issue, you have a couple of options:
Share the file in CORE with everyone on the call, so you can look at it concurrently.
Participate in a Sync Session. As the presenter, turn on Review Mode in your package and invite all on the call to join the session, by turning on Review Mode, as well. As the host, you can "drive" what everyone sees.
See more information about Sync Sessions.