With the student subscription, you can use try the services listed here.
GPU Optimized VM's are the N series VM's. By default the quota on the subscription for this type of VM's are set to 0.
In order to use the N series VMs, you need to submit a request to enable these series for your subscription (if your subscription supports).
Request a quota submission here for the VM available region.
Incase you want to move to pay-as-you-go offering, please check the details here.
Similar issue: https://stackoverflow.com/questions/65060958/moving-from-azure-for-students-to-pay-as-you-go
Hope this helps.
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