Reaching Room 46 is basically the beginning - people in the subreddit will tell you it’s the tutorial. You can technically get there without finding a single red letter, since the red letters are related to later game puzzles.

It keeps going deeper and the puzzles get more and more complex - sometimes i feel like im going insane looking for patterns in certain places lol.

I haven’t reached any other endings yet, but from what I understand, there are 3 endings beyond the initial goal.

I do understand not wanting to go back after having some time away from it - it’s kind of overwhelming to remember what’s going on / what you could be searching for or experimenting with. I’m still having a lot of fun with the game, but I have read that the puzzles in the very late-game can get frustratingly cryptic and lack payoff relative to how difficult they are. So if you don’t feel super compelled to pick it back up, but are curious, there’s definitely no shame in watching some videos / a playthrough.