So in a given turn in combat, you can interact with an item once per turn for free, then any subsequent interactions with the same or another item costs an Action (which, unless you can Action Surge or are hasted, this is your only Action).
Is drawing an arrow from a quiver to fire it from your bow an item interaction, or is this just part of the Attack Action with the bow?
For example, let's say I have a Ranger (low level, so that he doesn't yet have Extra Attack, not that it should affect this question, but let's keep it simple anyway) and he has a longbow and a shortsword. On his previous turn, he drew his sword with his free item interaction (whilst his bow was still in his other hand, since it only requires two handed to use, not to hold) and slew a nearby enemy that was badly injured (not worth an arrow).
Combat continues and it's his turn again; he wants to sheath his sword and fire at another enemy at distance with his bow (which he's still holding). By sheathing the sword and thus using up his free item interaction, can he now not draw an arrow without wasting his Action, thus not being able to actually fire the arrow?
Also, I'm aware of the "drop the sword" option, but this situation is illustrative of the rule I'm trying to discern, so I don't care about how to actually have him fire an arrow or not.