Aaaah I didn't see the torn label corner! Looks like it got me to the ending screen after messing around with the bottle too many times and accidentally getting the right dosage? ^^' Replayed right now the supposed way and it works fine!
Yeah, the rest of the interactables are pretty clear, for me it was just the bottle part. Did try to click everything at first, but soon noticed the only things I can interact with have a white outline, so I kinda was looking specifically for that indication by that last screen. I played a lot of point and click in my childhood, I think they usually blend the clickable items in the background, but show a highlight aura or change the cursor shape when you aim at them for visual feedback.