Port 7000: AirPlay
Port 7000 is used by AirPlay receivers, including Apple TVs, HomePods and Macs with AirPlay Receiver turned on.
What runs on port 7000
Apple's AirPlay protocol uses TCP 7000 for control and streaming to receivers, found via Bonjour. Since macOS Monterey, Macs can act as AirPlay receivers too, listening on 7000 and 5000. Apache Cassandra also uses 7000 for communication between database nodes.
On a home network
Apple TVs, HomePods, AirPlay-compatible smart TVs and speakers, and Macs with AirPlay Receiver enabled listen on 7000.
If port 7000 is reachable from the internet
AirPlay is a local-network feature and should not be reachable from the internet. Researchers have disclosed serious flaws in AirPlay implementations, including in third-party speakers and TVs, and a receiver exposed to the internet would put those in reach of anyone. Inside your home it is normal.
How to check whether it is open on your network
On a Mac, AirPlay Receiver is under System Settings, General, AirDrop and Handoff. RECON's LAN Scan and Port Scan show which devices answer on 7000.
To find out whether port 7000 is open on something in your home, and whether the internet can reach it, the app scans your Wi-Fi from your phone and checks your public address from the outside. It says what it checked and what it could not. Get RECON for iPhone — one-time purchase, no account, nothing leaves the device.