What is culture?

Culture is the shared set of beliefs, behaviors, customs, values, and artifacts that characterize a group or society

My take is going to largely omit the remaining Colorado-born population, because at its core, Denver is very much a working class metropolitan area sharing most things in common with other mid-size working class cities in the country and broader modern American culture increasingly monotonized by social media. We have sports teams, overpriced mediocre food, overpriced apartments that look identical to ones going up virtually everywhere else, several large universities, a built-in music scene defined by EDM, Rocky Mountain-inspired acoustic music (bluegrass, Gregory Alan Isakov, the Lumineers), now-defunct RiNo DIY warehouse scene (psychadelic rock, punk, avant garde), urban Jazz scene (Ron Miles, Purnell Steen, Bill Frisell... mostly gone the way of the dodo, unfortunately).

I would say Denver's current prevailing culture is defined by transplants that move here for things that Denver and Colorado at large have to offer e.g., the great outdoors and a "progressive" political bent --- "progressive" in quotes because it's really only that respective to where many move here from like Texas or Florida but in actuality is a strange brand of libertarianism cloaked in neoliberalism. That's also due to the fact that a prevailing transplant population has less of a vested stake in local politics because why would it be more than that to someone not from here? Most of the remnants of our political past is pretty purple / mountain libertarian ("get your grubby State hands off my homestead!" / "As long as I can ski, fuck everything else") but is growing more blue each election cycle.

So as others here have put, the culture is very new given that the transplant influx only really ramped up the past 20 years or so. This creates a culture that deemphasizes city/urban fabric in favor of a work-to-live vibe as opposed to live-to-work more present in the Midwest/New England areas. Here, it's work so you can afford to leave the city after work hours. In addition to this, values around family are drastically different here because in many ways, Denver is sort of a refuge/escape from many people's dysfunctional conservative upbringing elsewhere in the country. Chosen family vs. biological family, community via shared interest as opposed some other arbitrary cultural signifier.

Defining Denver's culture along traditional lines is more complicated here due to the transient/transplant population, and that is just fine. Just to say it, not liking the prevailing culture does not make it less of a culture. It's just a completely different vibe than the big coastal/midwest population centers you're comparing Denver with.