This has been irking me for the past couple of days. I would come back to my laptop (Lubuntu) after a period of time away and I would find Zoom (the video meeting app) open. I use Zoom for work, so I just dismissed it as a screen that I had forgotten to close. After seeing this for a couple of days, I realized something was wrong.
Luckily, some brilliant genious has tracked this issue down. Basically Zoom is also the name of a screensaver and is in your XScreensaver conf. For ubuntu I had to edit the etc/X11/app-defaults/XScreenSaver file, do a search /zoom and remove that line. Done!
For other flavors of linux, read the article above.
Hope this helps!
Thank you