Referred to as "Dwell Time" - the amount of time someone spends on a page or site - is not a ranking factor for Google - at least according to Google

Similarly, Bounce Rates, Scrolling, Pogo-Sticking and other similar engagement metrics are not used. Ask an SEO, and you'll get different answers!
However,
correlation does not equal causation.
Just because it looks like it happens, it doesn't mean that it actually does. People spend more time on a page because it's proving useful information to the user, and that's what affects the rankings.
Here's how we know it's not a ranking factor - not every website in the world uses Google Analytics. So Google can't 100% determine what people are doing on a site. They could be watching a video for 4 hours, they could have walked away from their computer. There's just no telling why someone spent "X" time on a page and truly correlate the data.
As far as personal experience in content, those are ranking factors, and that's confirmed by Google. They want more than just the facts; they want real-world experience (EEAT - Expertise, Experience, Authoritativeness, and Trustworthiness). I've not heard directly that smiles and similar emoji affect ranking, but they can affect the mood of a reader, and keeping them engaged so they read more is usually beneficial (not a ranking factor, beneficial that they'll purchase your product, believe your content, take action one something).
That's my take on things.