My experience on this matter is that GPU’s are allowed for free tier(credit card added). However, when you’re building a preemptible instance, your VM just does not start or it starts and by the time you SSH into it, it just stops. This was not my experience last year. I’ve not tried non-premptible instance yet. I’ll update once I try it.
It seems preemptible instances are not allowed on the free tier. Thanks to @Harvey for the info. Leaving a link from another thread.