If you want your customized Zoom background has a good performance, this is a recommended size for image background: 1920px X 1080px at an aspect ratio of 16:9.
Best size for customized virtual Zoom background? The minimum size requirement of the Zoom background image is 960px and the maximum size is 1920px. Besides, make sure your device meets the minimum system requirements to use the Zoom virtual background feature.
Or you can update the Zoom app to be the latest. Zoom virtual background not showing? If the virtual background is not showing up when you start the Zoom meeting, you can go to Settings > Meeting (Advanced) to turn Virtual Background on.