Played solo in desktop Chrome on a Windows laptop, with a fairly short browser window (about 640px tall). I only got part of the way, and the reason is probably the most useful thing I can tell you.
1. Where I first felt unsure: straight after taking the key. The message says to select it below the scene, but in the embedded frame the satchel was below the visible area. Scrolling the mouse wheel over the game moved the itch.io page instead of the game, and dragging the game's own scrollbar did nothing for me, so I never got the satchel on screen. On a taller screen this may never come up. Putting the satchel beside or on top of the scene, or making the frame shorter, would avoid it.
2. Selecting and using an item: I cannot judge this, because I did not reach the satchel.
3. Ending: not reached, no hints used.
4. What I would change: after I took the key, the line under the scene still read that an envelope waits on the stone bench, and the envelope kept its marker. Updating that line to point at the door would have told me what to do next.
What worked: the diamond markers made it obvious what could be clicked, and opening the letter and taking the key was clear with no instructions. The writing and the look of the first scene set the mood well.