Apple Support reached out to me that the problem has been resolved as of iOS/iPadOS 15.1
Happy to report that iOS/iPadOS 15.1 does indeed put back the "Apple TV Keyboard" under "Settings | Notifications". And, it does indeed work. When off, no more notifications to any of my devices that are logged in to the same Apple ID as the Apple TVs. So family members can use Apple TV now without disrupting others' devices.
Thanks again to MacRumors staff for bringing awareness of this issue. No doubt it helped to put pressure on Apple to fix it sooner than later.
Happy to report that iOS/iPadOS 15.1 does indeed put back the "Apple TV Keyboard" under "Settings | Notifications". And, it does indeed work. When off, no more notifications to any of my devices that are logged in to the same Apple ID as the Apple TVs. So family members can use Apple TV now without disrupting others' devices.
Thanks again to MacRumors staff for bringing awareness of this issue. No doubt it helped to put pressure on Apple to fix it sooner than later.