Re: What about UK ?
Apart from narrow area’s in inner cities, stations, airports, hotels and conference/event centres where tall building will screw with signals anyway the ROI of hundred’s of mini-masts will never allow them to be deployed so mmWave will be just marketing puff
However, those are the places that will truly benefit from it. Pre-covid rush hour, or at sports/concert arenas have been historically poor for connectivity because of all the people. Out in the woop woops, you don't need that sort of service, regular 4G/5G would suffice.