I can not share content from your Apple devices to your Apple TV, AirPlay 2-compatible smart TV

1. Verify that both devices are connected to the same home network.
2. Verify that the content (/app/service) streams in a format compatible with AirPlay. Usually, they will list AirPlay compatibility on their website. If not, ask them. Enabling AirPlay is a content provider decision. They may block it, they may have minimum system requirements.

Use AirPlay to stream video or mirror the screen of your iPhone, iPad, or iPod touch - Apple Support

If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support

From what device are you trying to use AirPlay?

Is this about streaming to your Apple TV HD?

What content (from what service) are you trying to use AirPlay with?