Which of your boards come with native USB C? I'm guessing that's the Thunderbolt models?
You don't make it easy to filter down to see which ATX models support Thunderbolt
Of the Z270 ATX boards, only the Supercarrier has Thunderbolt 3 with two type-C connectors. The rest are USB 3.0 or 3.1. Full list below:
USB 3.1 type-C boards (ATX):
Z270 Gaming i7
Z270 Taichi
Z270 Gaming K6
Z270 Extreme4
All other ATX boards (B250/H270 included) are USB 3.0 (but still have type-C connectors)
USB 3.1 type-C boards (mATX):
Z270M Extreme4
All other mATX boards except B250M-HDV are USB 3.0 with type-C.
The Z270 Gaming-ITX/ac also comes with one Thunderbolt 3 port with a type-C connector.