USB 3.1 is a data transfer protocol with a maximum speed of up to 10 Gbps, twice that of USB 3.0.
Are USB 3.1 and USB Type-C the same?
USB-C or USB Type-C is created as a standard for the connector port so it does not know how to send data, process input and output signals like how, must send data where after processing.
That is the task of data transmission protocols, and USB 3.1 is one of those protocols.

USB 3.1 can be used with either USB-C or USB-A connectors, depending on the manufacturer's intention.

USB 3.1 is backward compatible with USB 2.0, meaning if you have a USB 2.0 hard drive connected to a computer with USB 3.0, it will still work, and vice versa. The speed will then reach the highest possible speed of the hard drive, not utilizing the full 5Gbps of USB 3.0.
Some images to identify USB 3.1

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