I've been trying to find an appropriate StackExchange site to come to, to ask questions about using, configuring, and troubleshooting my Samsung Gear S3 smartwatch. This seems to be the closest fit so far. Would it be on-topic here?
I'd say yes. We already have some questions about smart watches. It might be dependent on the specific question how welcome it is but I consider wearables and smart watches part of the Internet of Things.
A smart watch is just a very compact computer - somewhere between a mini-PDA and (for those with their own mobile radio) a mini-smartphone.
As such, it would only be on topic here when used for an IoT purpose.
The simplest was to tell if a question would be on topic would be to consider if it would be on topic if you replaced "smartwatch" with "phone" or "laptop"
- Using a smart watch to control the lights in your home.
- Using a smart watch as a bicycle computer
- Transferring calendar events from phone to smart watch.
- Backing up personal data from a smart watch
Getting sidetracked into general smart watch user support would be as far from the mission of this site as getting sidetracked into everyday smart phone, laptop, or TV support would be.