Hi,
After some research, I didn't find information about any limitation of storage pool size in Windows Admin center. And since we are hardly to have the similar environment to test for you. If you would like to do further research about this issue, it's recommended to open a case with MS.
Below is the link to open a case with MS:
https://support.microsoft.com/en-us/gp/customer-service-phone-numbers
Thanks for your time!
Best Regards,
Anne
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