Hello Robert,
For basic gravy, I use flour and butter (roux) then add the liquid slowly while whisking.
If I want a soup to thicken I use a cornstarch slurry (which I also add to large portions of gravy if the roux is not thinking it enough) You can add as much cornstarch slurry as needed to get the desired thickness if you’re making 6qt pot of soup, you need more than if you’re making a 4qt pot of soup. If it’s a cream soup like chowder add in some heavy cream so the consistency will result in a velvety creamy soup. If you want to chicken soup to the consistency of stew start with 2 tablespoons cornstarch mixed with 1./4 cup or more water so you’re able to mix it smooth and drizzle it into the simmering soup.
Flour added to a soup will taste like flour unless you cook it first, as shown in the photos I have of making the gravy from a roux, that is why cornstarch works really well in soups. Cheese sauce tastes better with a roux and the consistency is better too.
So my go-to rule of thumb is if it’s a gravy or cheesy, or creamy soup, start with a roux, if it’s a clear “sauce” like Chinese food sauces or soup, no need to use a roux a cornstarch slurry will work well.
Hope that helps!

I have more thickener ideas for soups here https://www.createdby-diane.com/2020/03/making-homemade-soup.html

~Diane