There is no technological limit within the StorPool software architecture to the number of flash drives used, just a best practice of deployment. Typical building blocks (storage nodes) have 10-24 drives installed, typically using 4-8TB NVMe. The number and capacity are tailored to the requirements of the specific end-user organizationss use case.
In general StorPool advices to use small nodes with 10-12 SSDs each, rather than small number of nodes with 36 or more drives each. The storage density and the overall cost are about the same, however a StorPool storage cluster build of smaller nodes is both faster and safer. It takes less time to rebuild a single node in case it fails.