Unless someone else has a better idea . . .

PowerPoint animates objects one at a time, it has not been my experience that it can differentiate how to animate lines of text within an object.

Therefore, if you want to have the first line appear separately from the following lines, they will all have to be individual text boxes.

If you want the 1st line to appear and then disappear before the 2nd line animates, then they will also have to be individual text boxes which you'll have to animate accordingly.