with TVos 17, you can see yourself singing on TV screen with Apple Sing. But your voice is still separated and not mixed with the sound track. Is there anyway to make it truly like a karaoke machine?
As your TV speakers or connected audio system will usually be pointed into the room, a microphone outputting to said speakers would give a feedback loop, destroying anything listenable. It is controllable on a good performing stage, but rarely in a living room, where the singer can’t get behind the speakers.
Some apps for iPhone suggest they will work with AppleTV and other products.
https://duckduckgo.com/?t=ftsa&q=karaoke+app+for+iPhone&ia=web
re: How to use Apple Music Sing: karaoke on iPhone, iPad and Apple TV | iMore
This goes on to suggest you need Apple Music and other things, too
[While few say much about 'seeing yourself' singing?]
Is it possible to use your iPhone as the microphone to sing to the Apple TV sing
