Q.‘cleaning’ soil for a flower garden bed
I have dug soil from an area where I would like a flower bed. I am in the process of screening this soil onto a tarp in hopes of being able to kill any weed roots in the screened soil before mixing in compost and returning it to the dugout bed. Can you advise of product available for this process. I have been keeping the screened soil with another tarp.

I wish i knew which weeds you are battling. Some reproduce from every bit of root left in the soil and some are heavy seed producers. Screening will not remove weed seeds, unfortunately. if you are sifting the soil, look for fleshy white roots; these are the most pernicious weeds. Since flowers often don't go into the garden until after your frost-free date, use early spring to see what germinates and remove it. You may want to use a pre-emergent when you set your plants out to keep further weed seeds from germinating. If growing flowers from seed outdoors, don't use a pre-emergent until after your flowers are up. I don't think there is a product that you can apply to the soil that will kill all roots and seeds. Anything that toxic will likely ruin the soil's health by destroying beneficial bacteria and fungi. This includes homemade products like baking soda and salt. You are doing what you can now; weeding is just a fact of life for gardeners. Soil that is heavily polluted with weeds may take a year of aggressive removal and several more years of weekly weeding to fully eliminate bad actors like mugwort and bishops weed.