Can the Immutable feature be added/chosen to Minio storage running on a Windows server from the Management console during bucket creation or afterwards (or from the Windows server after the bucket has been created)?

It's not supported for S3-compatible storage destinations yet. For Amazon S3, Wasabi, and Backblaze B2, it's only possible to enable object lock (immutability) during new storage new bucket creation only and can't be changed later.