@Maxwell Gilbert Thank you for reaching out to Microsoft Q&A. Immutable storage support for accounts with a hierarchical namespace is now Genrally Available. Her eis the list of Supported Configurations-
Unless you are enabling Version-level scope, HFS is supported otherwise. Also please note that as show above, Immutability policies are not supported in accounts that have the Network File System (NFS) 3.0 protocol or the SSH File Transfer Protocol (SFTP) enabled on them.
If you are enabling Container-level scope and having issues, please share the steps you are following so I can assist further. Thank you!