A phone playing a video would not be sufficient to establish that you were at home, but merely that the phone was powered on somewhere. But if YouTube had records that indicated your phone was connecting using an IP address at your home, then the phone’s location could be ascertained.

But that still doesn’t say anything about where you are, since not everyone – even in 2025 – carries their phone every time they leave home.

But if YouTube also registered a Like on a video at a particular time, and it can separately be proved that no one else could be at your house and no one else connected to your home network, and that your phone was not modified in such a way to fake such an action (eg a VPN), then this would be enough circumstantial evidence to convince a jury that you were probably at home.

And if home is nowhere near the murder scene, then this could be a defense.

Maybe. As you can see, a lot of "if"s are needed to string together an alibi, let alone a good one.