Highly unlikely this is what the civil war would be like. It’s not a state v state thing necessarily although that might be a small part of it. In the first civil war, the south unified and its people largely supported the war, except their slaves. It’s unlikely something like that will happen again. It’s not impossible but unlikely.

What is much more likely is rural v city. Even in red states, cities are blue and will often vote for blue policies. Rural areas are where things get dicey. They’ve been largely left behind by the surge in industry and general expansion of the capitalist economy we currently have (they’ve had a lot of businesses (including grocery stores) close because more people are leaving, and their rural towns are frequently having their hospitals close leaving large swaths of areas where the nearest hospital is an hour away). As such, they’ve got a grudge against the cities. What’s likely to happen is rural counties and their local governments trying to cut off their food supply, starving the cities to win the battle. There’s tons more possibilities, but this one I think is the one that’s got the highest likelihood.

Another possibility that is scary, but is highly dependent on the party of the people in power, is the government using their power to actually strike the cities, like in Syria where Assad bombed and used chemical weapons on his own people. Syria is actually a pretty good example of what more modern civil wars are like, or can be like. Governments v rebels and militias, and cities v rural (although there’s much less rural land in Syria).

If you’re interested, the podcast It Could Happen Here has a great first season where they go over possible disasters including a civil war and a pandemic (it was actually made in 2019 so before covid). It’s really helpful and can teach a lot, especially for an outsider from across the pond. It also does a lot better job giving an explanation and actual sources.

Hope this helps since it didn’t seem like you were getting a real answer.