Thanks for the feedback, and for playing!
Yeah, in hindsight I think it might have been good to be a little more upfront with the chair and separation mechanics.
As for the key...
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If you're referring to the Fragile Key, that's actually entirely optional. There are multiple routes/solutions to the room (kind of functioning as difficulty options) but the only required item is the Golden Key, which should be reachable no matter which route you take, even if you skip the Fragile Key.
(...Assuming I didn't miss a softlock, anyway, which isn't impossible. But I tested this area pretty hard, so it should be true.)
Thanks again for playing and leaving feedback! Glad you're enjoying it overall!