The symbol in between the time and the user icon indicates that it tried to connect to Wi-Fi, but failed to get a connection. One would use the Apple TV Remote to navigate to Settings, then Network, and find the Wi-Fi for your home network there.
Presumably it tried to automatically use the same network credentials as before, but the new modem may require new different connection settings.
The software remote on iPhone works over the home network, so that won’t be functional until the Apple TV box has a functional network connection. You’ll need to use the physical remote until then (which uses Bluetooth for the navigation controls, so the Wi-Fi network doesn’t matter for that).
If your Siri Remote or Apple TV Remote isn't working - Apple Support
- Try charging the remote (see below),
- Try pairing the remote again, using the indicated button combination,
- Try restarting just the remote, using the other indicated button combination,
- Try restarting the Apple TV box, by temporarily disconnecting from power.
Charge your Siri Remote or Apple TV remote - Apple Support
- Charge with a USB cable directly to a computer USB port, or to a USB power adapter in an AC socket,
- Other types of USB ports may not be suitable for charging this model remote,
- Charge for 30 minutes to charge from nearly discharged to well over 50% battery charge level, which should be enough for a while,
- Charge for 2.5–3 hours to charge from nearly discharged to 100% battery charge level,
- There are no visible indicators for charging on the remote itself.
