I was experiencing the same issue with AirPods 1 on macOS Big Sur. Enabling the AirPods microphone (so the headphones starts using the lower latency codec) fixed it. It looks like Google Meet doesn't like adjusting the audio latency, resulting in the garbled sound.
They will have seamless switching as of iOS 14, iPadOS 14 and macOS Big Sur.
When your other devices are signed in with the same Apple ID as your iPhone, AirPods automatically switch between your iPhone, iPad, iPod touch, and Mac.
For example, if you’re listening to another device with your AirPods but you want to listen to your iPhone instead, start ...
Spatial Audio is only used for video:
Spatial audio with dynamic head tracking brings a theater-like surround-sound experience to the movie or video you're watching...
You can confirm if the content you're listening to supports spatial audio by toggling it off and on: