Millimeter waves (30-100GHz range) attenuate like crazy & are seriously degraded by pretty much everything (eg: rain, dust).

For folks who must fret over mm wave tech, it's worth considering that cell towers have been using 11-83GHz bands for short distance backhaul & linkage for decades. So have tons of other industries.

Last, I'm about positive that only some approved frequency groups in the 5G standard will be in use, in any given region. Lower bands should see the widest deployment.