They has grown enormously as Apple used its monopoly power to make every other advertiser less effective. Apple still uses the same user targeting they banned for every other advertiser, of course.
Do they track your activity in non-Apple apps in order to feed their ad selection algos? I really don't know, but I would guess not, and that's the thing they banned for others.
(FWIW I find their move into ads alarming because it threatens to ruin everything I like about them)
(FWIW I find their move into ads alarming because it threatens to ruin everything I like about them)