How accurate are smartwatches?

Depends on the question you ask a watch, smart or dumb they will tell the time accurately twice a day if like mine it’s broken.

Not accurate, I’d say. Mine is always telling me to stand up when I’ve been standing for a while. 😒

I have read a research saying that they are not as accurate and can lead to orthosomnia

As accurate as my gaydar

Yes I have a Fit bit and it is pretty accurate although there are sometimes when it's not. Anytime that your hand that you wear the watch on is moving a lot it may count as steps and also the sleep is pretty accurate
By the way not all are created equal