The preview looks convincing while you sit still. Then you lift a mug and part of your hand disappears, or the room shows around your hair. Before an important call, test the movements you will actually make.
Check the effect your device supports
Zoom separates requirements for image and video backgrounds, with and without a physical green screen. Video backgrounds and backgrounds without a green screen can need more resources. A working camera does not mean every effect is supported.
Blur is not automatically a low-resource fallback: Zoom applies its image-background-without-a-green-screen requirements to blur too. Check the current requirements for your operating system and processor rather than choosing by the effect's name.
Use the camera, app and room lighting intended for the call. Turn your head, move your hands, hold up a plain object and lean slightly to each side. Watch the outline as well as whether the video freezes.
Prepare a simple alternative
If the effect breaks up or the computer struggles, try turning the effect off and compare. A tidy real background may be easier than finding another filter. Close unnecessary demanding applications when practical, then repeat the preview.
Remove documents or other details that should not be visible from the camera's view. A virtual background should not be your only way of hiding them. Recheck after changing the camera position or lighting. If the preview is smooth but participants report interruptions, investigate the connection separately; background processing and network quality are different things to check.