I've been researching this. 1. Glyphosate (roundup) use is two orders of magnitude higher than originally approved. 2. Due to the emergence of glyphosate-resistant weeds, the dosage has been increased substantially. 3. It is now also usually combined with other compounds to increase effectiveness, which affects how it breaks down and affects both the food and environment. 4. It is now also used for 'green burndown'.…
As to the science: the original highly-questionable IARC determination has since been contested by both the European Chemical Agency and the European Food Safety Authority.
It doesn't do us any good calling everything in the world a carcinogen. We have to rank-order risks in order to make reasonable choices in life, and glyphosate sits very low on that list compared to other industrial chemicals when you look at the evidence for mutagenicity or secondary carcinogenic mechanisms.