Welcome to the forum @digitalskillz! According to this article from a Canadian site it should have 727 liters (25.7 cubic feet) behind the third row seats and the maximum space with the second and third row sears dropped is 2,144 liters (75.7 cubic feet).
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On paper at least, the GV80 claims to have more cargo space than two of its key competitors. The minimum space behind the third row measures at 727 litres, as opposed to 650 in the BMW X5 and 630 in the Mercedes-Benz GLE. Maximum space in the GV80 with both the second and third rows dropped is 2,144 litres, while the BMW tops out at 1,870 and the Mercedes at 2,055.

Ministry of Interior Affairs: 2021 Genesis GV80
The Genesis GV80's premium features and finishes for a lower-than-average asking price is certainly an attractive proposition
driving.ca
On paper at least, the GV80 claims to have more cargo space than two of its key competitors. The minimum space behind the third row measures at 727 litres, as opposed to 650 in the BMW X5 and 630 in the Mercedes-Benz GLE. Maximum space in the GV80 with both the second and third rows dropped is 2,144 litres, while the BMW tops out at 1,870 and the Mercedes at 2,055.