Diagnosis
You can't use a stereo pair over Bluetooth. Bluetooth only supports a single audio stream to one speaker at a time from a computer.
How to Fix It
For a stereo pair, you must set them up as such in the Google Home app (under 'Create speaker pair'), then cast audio to them via Chromecast built-in from apps like Spotify or YouTube on your computer. Do not use the Bluetooth connection for paired speakers.
If That Didn't Work
If you only need one speaker for your computer, forget the Nest Audio from your computer's Bluetooth device list. On the speaker, say "Hey Google, Bluetooth pairing." Re-pair it fresh from your computer, keeping them within 3 feet during setup.
Heads Up
Bluetooth on Nest Audio is primarily for initial setup and casual phone audio. For reliable, high-quality audio from a computer, using Chromecast (via compatible apps or Chrome browser tab casting) is the intended and more stable method.