Most drives that accept a USB-C cable are USB-3 drives, unless they were tested, qualified, advertised, and sold as ThunderBolt-3, and have the ThunderBolt logo near their data port.
USB-3 drives do not require the "heavy artillery" of the Apple Thunderbolt-3 <-> Thunderbolt-2 adapter (and an additional genuine ThunderBolt-2 cable if there is no captive cable on the device).
You can connect MANY devices through that adapter, but it does not provide power in either direction, so the devices must have their own power supply.
About the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple Support
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