A "World War" probably isn't characterized by its "size" (whatever that means) but rather by the fact that the combat theatre extends over much of "the world", or that much of "the world" are active belligerents. Ukraine is right now a localized conflict; I don't think it counts.

FWIW, as one potential size metric: casualties in Ukraine (so far) are comparable to the Korean or Vietnam War, and an order of magnitude less than the World Wars (even though the world has roughly 4x the population now than in 1939). It's much more comparable to those conflicts than either of the World Wars.