Research Square is a platform for preprints. These are not regarded as publications, therefore there cannot be any Impact Factor etc. See also: https://www.researchgate.net/post/What_is_this_research_square_doing
I agree with the comment by Dr Wolfgang R. Dick that there is no IF, etc. With regard to your question about why forced, that has never happened to me before with them. It has happened with another publishers I have found and I take two possible approaches. (1) ignore their emails or (2) use opt-out. Or both!
As we know research Square is a platform that offers a range of services to researchers, including preprint hosting, manuscript editing, and journal submission support. It does not force researchers to join its team or submit their papers.
Researchers have the freedom to choose whether or not to utilize the services offered by Research Square.