https://arstechnica.com/information-technology/2021/04/verizon-leads-all-us-carriers-in-mmwave-5g-availability-at-0-8/

US mobile customers are almost never able to connect to millimeter-wave networks even though the cellular industry and Verizon in particular have spent years hyping the fastest form of 5G.

AT&T and T-Mobile customers with devices capable of using millimeter-wave networks were connected to mmWave 5G only 0.5 percent of the time during the 90-day period between January 16 and April 15, 2021, according to an OpenSignal report released today. Even on Verizon, the carrier with the most aggressive rollout of mmWave 5G, users with compatible devices spent 0.8 percent of their time on the high-frequency network that uses its large capacity to provide faster speeds than low- and mid-band spectrum.