While you can set up and use the downlight over Bluetooth with the Nanoleaf App, it must be used over Thread to fully utilize its Matter capabilities and connect to other smart home ecosystems.
With Thread, you get the benefits of improved reliabilty, faster speeds, fewer dropped connections, increased range, and lower power consumption. You'll also unlock usage of the Nanoleaf Desktop App and the Screen Mirror feature.
Running Matter over Thread allows you to connect your downlight to your smart home ecosystem, control it with voice commands and gain remote access and additional customization features.
[A Thread border router is required to use Thread, and a smart home hub is required to run Matter over Thread]