Possible and not possible workloads on Azure Stack HCI

yes, you can run pretty anything on Azure Stack HCI except your software vendor makes restrictions that do not apply within the limits of Azure Stack HCI - which are quite high. Ask your SAP partner. I have seen at least one customer running SAP workloads on Azure Stack HCI.

there is at least one that is not supported. The Azure Stack HCI nodes need internet connectivity outbound via https to Azure. At least every 30 days, so same like M365. If you cannot manage this through dynamic rules / URL filtering etc. any you may not open this connection once at a time, then Azure Stack isn't the right thing. And you need even more connection if you want to get the best out of Azure Stack HCI using Arc enabled services (automated patching for VMs and Hosts + Firmware + Drivers, Disaster Recovery, Security, Monitoring, Azure Policies, Containers etc.