Tv turns off immediately after turning on

When you turn on your Apple TV with the remote, it can send zero or more signals to your Sony TV to tell it to “change power state / turn on or turn off”.

It can do this is two ways:

• send a signal over the HDMI cable “HDMI-CEC”
• send a signal from the Apple TV remote’s “IR emitter” to the TV

This article from Apple can help explain more:

If you can't control your Apple TV with your home theater or universal remote - Apple Support

It kinda sounds like your Apple TV remote is sending a “turn on/off” signal to the TV when powering up - but it’s a bit hard to tell.

These steps could help narrow down the issue:

• With the Sony tv off, use Siri on your phone to turn on the Apple TV “hey siri turn on Apple TV” -> if this works properly, then the Apple TV remote is probably configured wrong (maybe switch the setting to hdmi-CEC instead of IR)
• Try changing the remote control setting on the Apple TV from hdmi-CEC to IR (or back the other way)
• With the Sony tv and Apple TV off, see if you can AirPlay to the Apple TV from your phone. -> this would suggest a configuration issue with your phone.
• HDMI-CEC has gone through many iterations - I’d manually update the TV (and any audio receivers you might have) to make sure they have the latest firmware.
• Play with the TV settings to make sure HDMI-CEC is turned on (or perhaps turn it off briefly to see what happens - perhaps it is getting commands twice somehow? Over CEC and IR?)