Actually, it's more the opposite. Sorry, I don't think I explained too well. The watch works just fine on its own without a smartphone. For functions that require phone and watch working together, Gadgetbridge lets them communicate (e.g. when you receive a text message on your phone, Gadgetbridge will let you read the text on your watch).

The apps on the watch will work with or without a smartphone. However, installing apps from the Bangle app loader requires the watch have a Bluetooth connection to a phone or computer. After apps are installed, they will run even without the Bluetooth connection.

Finally, note that the Bangle does not have an internet connection on its own; it has no cellular or wi-fi radios on board. So any apps that require a network connection (e.g. weather) will only work when paired to a phone with Gadgetbridge. I think there are other watches with wi-fi, but I'm not familiar with them.