The big problem with this issue is both sides have deeply vested interests in their entrenched positions. They are unwilling to sit down and have an honest discussion about how to objectively determine the real environmental impact of using ethanol. On the one side, as has been noted, are farmers and ethanol producers. On the other side the NAS study,
https://www.pnas.org/content/119/9/e2101084119, was funded in part by the National Wildlife Federation. The NWF has done a lot of good work protecting wildlife, but they are adamantly opposed to converting ground from wild and native vegetation to farm crops. That is one of the key points in their study. We have seen the impact here in Idaho where game birds such as sage grouse and pheasants are teetering on the edge of population collapse since so much of the previous vegetative cover they depend on has been replaced by crops.
In this pro-ethanol article,
https://www.agriculture.com/news/crops/industry-experts-say-new-ethanol-study-not-worth-their-time, the claim is made that the author of the study has been previously discredited and has not accepted an offer to sit down and discuss the issue. What I gather is the two sides simply do not agree how carbon impact should be determined.
My observation in life has been that when either party refuses to rationally and objectively discuss the reasons for their stance on a subject, they know their position is not 100% defensible.
Is ethanol use bad for the environment? In some ways, yes. Is gasoline use bad for the environment? In some ways, yes. Which one is worse? We do not know because advocates on both sides refuse to know. A somewhat related example is sprinkler irrigation vs flood irrigation. Sprinkler uses less water, so it's better that way. But it returns less water into the aquifer. So for replenishing the aquifer flood is better. But it uses more water, and much of that water gets dirty and eventually flows into rivers, raising the contamination levels. What's the best answer? I'm not sure there is one!