Nonsense. It's visible under the Network panel. Same as with any other device with a network adapter. For devices that have both WiFi and wired connections, there's a different MAC address for each one.
To quote from the Wiki page:
A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment.
MAC addresses are primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address, or as an Ethernet hardware address, hardware address, or physical address.
The MAC address is unique to each network adapter, although some devices allow spoofing the MAC address. Roku devices are not included in that ability.
EDIT: let me rephrase that. You can't get to the Roku menus until the device is registered, so that is correct you can't see the MAC address until it's registered to the Roku user account. But the MAC address is already there assigned to the device before it's ever connected to the network. If you must have a MAC address to allow a device on a network, then you can use a phone hotspot to complete the registration and then access the MAC address to allow putting it onto a restricted network.
