TVs that are homekit compatible will let you control power and input from homekit.
You can control homekit devices using the home app on your phone, iPad, or Mac. As well as Siri from any device that has it. There are also a few third party homekit apps that all have mostly the same features as apple's home app, but their interfaces are laid out a little differently
There are numerous homekit devices, things like smart bulbs that let you pick a color, or light switches and plugin modules that will let you control your existing lamps, as well as thermostats, window shades, home alarms, and door locks. There are also many types of sensors available --- temperature, humidity, motion, door/window.
You can make scenes in homekit that let you set a specified state for your devices.
So you could make a "good night" scene that turns off the TV and all of your lights, as well as locking the doors and turning on the alarm.
Or a "gaming mode" scene that sets a dim look on your lights, and turns the TV on, and changes the input to HDMI 3.
Siri can play scenes just by asking for them by name so "hey siri, goodnight" will play that scene.
If you have an appleTV or HomePod, those will allow you to control your homekit devices no matter where you are, as long as you have Internet. So I can turn my lights on or off, or set the thermostat even if I'm at work.
You can also make automations, so if you have a door sensor, you could have a light automatically turn on when that door is opened.
You can also have it alert you if a door opens or a motion sensor triggers and you're not at home.
for both automations and notifications, you need an appleTV or HomePod.