Any more hints? I can’t seem to find it.
SPOILERS BELOW
I see some openings at the top, but one I can jump in to but just fall back down and reset the level, the other in the next room I can’t reach.
Further hint (bordering on, or crossing into full spoiler):
Assuming you are missing the one that I was - (and it sounds like it) the one hidden off the mimic room - there's two adjacent rooms with openings in the ceiling. One of those openings is hard to see because it's actually a ladder, so due to certain UI choices it kind of blends in with the ceiling. You need to reach that, using the blocks in the room and climb, not just jump up.