The AT&T 6 model has mmWave as well. It's the T-Mobile and unlocked versions that don't.From what I understand:
All Pixel 6 Pro in the US support Sub6 + mmWave, (Whether a carrier allows access on unlocked models is unclear)
Regular Pixel 6 is Sub6 Only except for the Verizon variant which adds mmWave.
This has never been an issue on Unlocked Samsung models. Each variant has a different SKU and it'd be interesting to find out if it's a different modem entirely or just software optimizations.
My only concern with the Verizon version is that it may not be bootloader unlockable.
The Pixel 6 Pro comes with mmWave on all US models.
Quite frankly this is stupid with the base 6 because T-Mobile has mmWave spectrum too and it's only a matter of time before they start rolling that out in places besides NY.