There is a site setting solved topics auto close hours. I think this would be a better default for the Auto close solved topics category setting.
To keep the default of closing after 2 days, the default of the site setting could be adjusted. But admins who do not want topics to be closed automatically would no longer have to change the category setting on every category they create, but only the site setting and categories created before they changed the global site setting. (An option to adjust existing categories when changing the site default, similar to user preference defaults, would be the icing on the cake.)