^Which "suburban" counties or areas are we talking about here? The three most Republican small-town/rural counties in NW Iowa (and the entire state) gave Trump a larger raw vote margin than all the counties bordering Polk County combined, even if we exclude Story County (which is easily the most populous and "suburban" of the nine, was more Democratic than Polk, and one of only four counties to trend Democratic in 2016). The second of the four counties to trend Democratic was Dallas County, the most populous Des Moines suburban county after Story, and this one even swung Democratic.
No offense (maybe I’m blind), but I don’t see how it’s inflexible Republican "suburban" voters in the Des Moines area which are contributing to Iowa's rightward shift in any noticeable way.
Especially when if anything, the Iowa “suburbs” are following the nationwide trend. Boone and Dallas counties have treated Dems pretty well recently. It’s just not nearly enough to matter since they are pretty insignificant on the overall statewide vote, unlike Georgia where Trump losing Gwinnett County by 20% (which is very possible by the way) would spell his doom.