You can found more information at the documentation Google Cloud Free Tier:
The Google Cloud Free Tier has two parts:
At the section 12-month, $300 free trial you can find Program coverage details:
Your free trial credit applies to all Google Cloud resources, with the
following exceptions:
- You can't have more than 8 cores (or virtual CPUs) running at the same time.
- You can't add GPUs to your VM instances.
- You can't request a quota increase. For an overview of Compute Engine quotas, see Resource quotas.
- You can't create VM instances that are based on Windows Server images.
You must upgrade your account to perform any of the actions in the preceding list.
In addition, have a look at the End of the free trial:
The free trial ends when you use all of your credit, or after 12
months, whichever happens first. At that time, the following
conditions apply:
- You must upgrade to a paid account to continue using Google Cloud.
- All resources you created during the trial are stopped.
- Any data you stored in Compute Engine is lost.
- Your account enters a 30-day grace period, during which you can recover resources and data you stored in any Google Cloud services
during the trial period.
- You might receive a message stating that your account has been canceled, which only indicates that your account has been suspended to
prevent charges.
and at the Recovering data:
Caution: There is no automated way to recover data that you used on VM instances you created with Compute Engine. You must manually
export any data that you want to keep from your Compute Engine VM
instances before the trial period ends.
I do recommend you to upgrade your account before free trial ends.