How to Pair your new Siri remote with your Apple TV.
https://www.avsforum.com/threads/new-apple-siri-remote-2021-owner%E2%80%99s-thread-faqs-user-guides-news-posts-1-5.3196795/#PAIRING
How do I pair a new Siri Remote with my existing Apple TV?
1. Turn on Apple TV and position the Siri Remote so it’s within 3 to 4 inches (8 to 10 cm) and pointing at the front of the Apple TV 4K/HD.
2. Press and hold the Back button (“<“) and Volume Up button ("+") buttons for 3 seconds.
3. When the Siri Remote is successfully paired, an onscreen message appears.
When you pair a remote, any other previously paired remote is automatically unpaired.
Sometimes, you may be asked to place the remote on top of the Apple TV while pairing, but the process is otherwise automatic. If your Apple TV isn’t detecting the remote, try charging the remote for 10 minutes and try again. If your Siri remote still isn't working.