I just came across this as well, and I think it is to do with the apiVersion being used when exporting the template from an already deployed resource.
I changed my templated to use 2019-06-01, instead of the 2021-01-01 that was being used for Microsoft.Storage/storageAccounts/fileServices, and deployment then worked OK.
Edit: Actually, that wasn't it. I removed the following empty sections from the template, and the deployment works. When this is put back in, it fails again regardless of the API version.
"protocolSettings": {
"smb": {}
},
"cors": {
"corsRules": []
},