I figured it out just before your message was posted, but thanks anyway:
Apple's summary:
Vehicle Motion Cues is a new accessibility feature in macOS Tahoe that helps reduce motion sickness by displaying animated dots on the screen to simulate the vehicle's motion. To enable it, go to System Settings > Accessibility > Motion and turn on Vehicle Motion Cues. You can customize the appearance, color, pattern, size, and number of dots to suit your preference.
Location of setting: System Settings: Accessibility: Vehicle Motion Cues is second to last in listings. It appears that it is on by default, even though my laptop rarely leaves its desk.
The dots, of course, were not animated as my desk/workbench weighs about 400 lbs.