Yeah, the headline is a little misleading/sensationalist, but also a little true. What it essentially means is that a person cannot sue a chemical manufacturer in a state court over negligent labeling (in this case the plaintiff alleged that Monsanto should have provided a warning on label about cancer risks) as long as their label adheres to what the Federal EPA has stipulated.

There is a type of product liability lawsuit called "failure to warn", where a person can claim that a product was missing critical safety information regarding the use of the product. In this case, Durnell's lawsuit was a failure to warn lawsuit, alleging that glyphosate gave him cancer and that Monsanto was liable due to not providing a cancer warning on the label, since having one would have directly influence his use of the product.

And he won in Missouri State Court with a jury trial. And Monsanto appealed it to the Missouri Court of Appeals the verdict was again upheld.

Ultimately it got appealed to the Supreme Court, with the argument that FIFRA preempts state law, in that it says that a state cannot require any packaging or labeling requirements in addition to or different from federal requirements. FIFRA also requires that all products carry the EPA approved labeling with no modifications.

And the Supreme Court agreed, ultimately ruling that Monsanto is bound by the regulatory directives of the EPA, and the EPA has not found that such a label is warranted. Monsanto is required by federal regulation to have the approved EPA label (they could not legally change it even if they wanted to, without going through whatever EPA processes are in place), and as such someone cannot sue at the state level under state laws arguing that something should be added to the label.

So it isn't really some form of blanket immunity, but it does mean that a company that has undergone the EPA regulatory process for their pesticide cannot be sued in a state specifically for leaving something off the EPA-required label that caused injury.

There are potentially other claims one could make, like negligent testing, design defect, misrepresentation, etc., but one can't sue over the label at the State level.

Ultimately the solution is regulatory and executive. Congress needs to better define liability (such as Rep Massie's No Immunity for Glyphosate bill: https://www.congress.gov/bill/119th-congress/house-bill/7601) and the EPA needs to do its due diligence with regards to product safety, since they are ultimately the gatekeeper of ensuring a product meets the environmental, health, and safety claims put forth.

Also, one more thing to make one's blood boil, this years Farm Bill actually contained a blanket immunity stipulation for pesticide manufacturers that a group of dedicated lawmakers fought and managed to get stripped out at the last minute. https://www.earthisland.org/journal/index.php/articles/entry/pro-pesticide-measure-cut-from-farm-bill/