How to open the unicorn door in Resident Evil Requiem

It doesn't get much more classically Resident Evil than a locked door with an obnoxious opening mechanism, and that includes how to unlock the unicorn door into the Parlor in Resident Evil Requiem. Who needs keys when you have secret boxes with hidden jewels hidden inside?

The hardest part about this puzzle is actually getting to the items you need, so to speed things along, I'll explain how to open the unicorn door in Resident Evil Requiem, including the location of the Unicorn Trinket Box, plus how to open that as well.