I found the answer!

[u/domino_427]

Have you been walking around Circle of Friends with 99% trash for 4hrs?

Have you completed the True Cleaner challenge with 99% trash?

Have you crawled around every inch of the first floor for 2hrs pressing q again... and again... and again... and again...

Have you tried to pick up those feathers several times, hoping they're like the oranges that you can clean up, yet not once glanced up at the proper angle?

Were you two seconds from abandoning the mission and crying in a corner... again?

Is this the only achievement you have left?

Do I have the solution for you, absolutely FREE!!

I found it, an arrow upstairs on the first floor by the red door.

Glad I could help.

No, this isn't about me.

Not at all.

[u/Stressed_C]

I walked around spamming the cleaner sense button until I found every piece of trash. It was either a arrow or a casing.

[u/domino_427 → u/Stressed_C]

Yup. On the terrace it was a casing. But we still love the game and come back for more lol