Hello DannnyB,
It sounds like you're concerned that a used Apple TV might be unusable due to an iCloud block of some sort. No, you cannot use iCloud to lock an Apple TV. According to this article it requires an iOS device, or Apple Watch:
Find My iPhone Activation Lock
Thank you for using Apple Support Communities.
It sounds like you're concerned that a used Apple TV might be unusable due to an iCloud block of some sort. No, you cannot use iCloud to lock an Apple TV. According to this article it requires an iOS device, or Apple Watch:
Find My iPhone Activation Lock
Find My iPhone includes Activation Lock—a feature that's designed to prevent anyone else from using your iPhone, iPad, iPod touch, or Apple Watch if it's ever lost or stolen. Activation Lock is enabled automatically when you turn on Find My iPhone.
Thank you for using Apple Support Communities.