First, since you already checked that the Macbook is on the same network, what version of the OS are you using and in particular, what version of iTunes? From what I could tell, you need to have version 12.7.3 of iTunes installed and I also believe, depending on how the HomePod is configured, that you may need to also be logged into the same AppleID or family member AppleID that is a part of your Home on the Macbook. However, first, here is how to check/change the HomePod speaker access settings:
1. Open the Home app on an iOS device.
2. Tap on the location icon (top left)
3. Scroll down to the SPEAKERS section
4. Look at the Allow Speaker Access setting. Mine is set to On Network
5. If it's not set to On Network, tap on the speaker access setting row.
6. Now choose Anyone On the Same Network from the list of speaker access settings.
7. Go back and confirm your changes.
8. You should now see HomePod from the Macbook