At the end of my playthrough, I noticed how I only had 19 golden feathers, so I tried to search for the missing one, but I couldn't seem to find it on my own. I looked through walkthroughs and followed along speed runs yet I still ended up with 19 of them, so I loaded up a new save slot to see if it could potentially be a bug. When I got to this rock: https://imgur.com/f95IbjZ, I noticed how the golden feather was missing on it (following the walkthrough). I hope the developer sees this so they could address the bug (this is on the latest version, btw). Nevertheless, I really enjoyed the game and found it such a wonderful experience :D Thanks!
*EDIT* I have now learned that the golden feather on the rock was moved, thanks so much for the reply below in pointing that out
*SPOILERS FOR HOW TO GET IT* You have to complete the 2nd boat challenge and it will be awarded to you by the fawn that rides with you