I actually completed this earlier in the week, and then completed it again a few days later. But they weren’t the proper endings – and today’s was. I hope. I can’t see anything else I may have missed anywhere, at least.
And yes, it was one of the most frustrating games I’ve played in a long time. Some of the puzzles were just too hidden, trial and error, convoluted, or abstract. But it does feel rewarding having actually beaten it!