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Basically yes.
But it depends on what you connect to the Uno's 5V and 3.3V pins and the pins configured as output.
The on-board voltage regulator converts the product of voltage drop (12V - 5V) and the needed current to heat and there is a limit to what it can handle.
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Vin is the input used for the 7V (or higher) power supply. It provides the same function as the barrel jack on the board.