The Slow spell includes this rule for any creature affected by it:
Regardless of the creature's abilities or magic items, it can't make more than one melee or ranged attack during its turn.
You can use your action to make a ranged attack against any number of creatures within 10 feet of a point you can see within your weapon’s range. You must have ammunition for each target, as normal, and you make a separate attack roll for each target.
You can use your action to make a melee attack against any number of creatures within 5 feet of you, with a separate attack roll for each target.
As I understand it, both of these abilities are considered to be a single attack, albeit with multiple attack rolls. Does that mean the Slow spell would not prevent a ranger from using either ability if they were under its influence?