Yes - I live in Austin on Verizon and it often shows 5G but is usually slower than my AT&T LTE was in San Francisco -- however -- occasionally I get 5G Ultra Wideband and got 1915mbps down this weekend https://i.imgur.com/BuQF13Y.jpg
> 5G Auto: Enables Smart Data mode. When 5G speeds don’t provide a noticeably better experience, your iPhone automatically switches to LTE, saving battery life.
Having used an iPhone 12 in an area with 5G service, I haven’t yet noticed the phone reporting LTE speeds, but given the way the statement above is worded (‘noticeably better’ is doing a lot of heavy lifting), I wouldn’t be surprised if the phone is mostly on LTE when it’s sitting idle or when I’m doing something like web browsing or music streaming that’s otherwise well within the capabilities of an LTE network.