When joining a meeting as an attendee, you can preview your video before you join. While previewing your video, you have the option to update video settings such as your virtual background or video filters. Additionally, you can test your video at any time when you are not in a meeting.
Note: If you are the host of a meeting, you will not be shown the Video Preview dialog before starting a meeting, however, you can test your video settings before you start the meeting.
Learn more about testing your video settings before a meeting.