DIAGNOSIS The motion detection is too sensitive or is being triggered by something you don't consider motion, like light changes from clouds passing by, shadows, or a flickering lamp.
FIX You need to adjust the activity zones and sensitivity. 1) In the Google Home app, tap your camera, then the settings gear. 2) Go to "Notifications" and then "Activity zones." 3) Draw zones only on the areas where you want to detect motion (like a doorway, not a window with passing cars). 4) Go back and adjust the "Sound and motion" sensitivity slider down a notch or two. Save and test for a day.
IF THAT DIDN'T WORK Look at what's in the frame. Indoor plants moving from air vents, a TV screen, or a pet in a different zone can trigger it. Reposition the camera slightly or use the "Familiar faces" feature to tell it to ignore your pets (if your Nest Aware subscription includes it).
HEADS UP Even with perfect settings, some false alerts are normal. The software is looking for pixel changes, and any change—like a big shift in sunlight—can register. It's a balance between catching everything and getting too many notifications.