We absolutely do have a common culture. The fact so many people think we do not is derivative of social media and smartphones.
All but the most extreme far-right and far-left people in the country really do agree on 95%+ of anything with daily relevance to their lives.
For a long time the number 1 song in the USA was "Choosin Texas" by Ella Langley.
I have no idea who that is and I've never heard the song.
That 95% number is so far from the truth. Gen Z males are significantly (though not majority) right wing and Gen Z females are the exact opposite. Based on data, 67% of the time, Gen Z males and females do not agree on the same political issues.
I don’t think the “agreeing middle” is 95% anymore. Maybe this is a Chronically Online POV but it seems the extremes are growing quickly, the center is shrinking, and society is going bimodal.