This is sort of a clarification from my last post. It's not that I can't interact with projectiles, the actual issue is that I can't interact with entities after they've been added to a scoreboard.

With players, I could add them to a scoreboard, then do whatever after a specific score is reached.

With entities, instead of names (because they're not players), it does this ID-sort-of thing.
Ex. a chicken would be called 99882be8-dee7-4a1f-b207-c8ab2cb75d9e.
Since this is not how entities are listed inside of entity_list('*') or similar commands, there's no way to interact with them using Scarpet commands.

Ooop, found out about query(e,'uuid'). I could run a for loop to search for the entity's UUID in the entity_list() output.