It seems that you CANNOT cancel the 30-day free Nest Aware trial subscription! Google Nest says:
"Once you start the trial, you can’t cancel it, but you can turn off your camera recording and sound detection if you want. You can also delete your video history and sound detection events with the app."
Thanks for reaching out. You'll not be automatically charged if you ignore the link included to your email and you'll not be automatically subscribed to the Nest Aware when you don't fill up the information such as, card information or your Google Pay account. In case you need to cancel it, just hit this link. Let us know if you have more questions in mind.
I appreciate the help, JT and MplsCustomer.