In The Slums 1, you can go straight from the lockdown cutscene to Seamus' apartment door. Sprint into the far right section of the door, where the doorjamb is. Eventually, the cat will glitch a little and you will be able to see the inside. Move the camera around, and he will go through the wall. Although Seamus isn't here, you can still pick up the broken tracker the same way as normal. Once you do, sprint at the right side of the door this time, closer to the right side of the doorjamb. Basically, try to hit where the door and the wall meet, and the cat will fly right through. Doing this allows you to skip collecting the book and all of the rest of The Slums and Dead End. Get the tracker fixed by Elliot, and immediately after (while you are in his room), reset to the last checkpoint. After the game loads, bring the fixed tracker back to Seamus' apartment by glitching through the door again. He will be waiting and will start the next level. The door, however, is still closed so Seamus won't be allowed to leave, so as soon as the next level starts, quit out of the game and select to redo The Slums 2. This skip saves about 5-7 minutes due to not having to complete The Slums 1 or Dead End.

*Skips the level Rooftops, not Dead End. My apologies

I can get into the apartment but am struggling to get out haha

This is referred to as slums skip in the discord

With Inputs and also how to leave

Jump Through Dont know if there is 100% way of doing this?

Hello, you can check this guy, at 18:35 :

Edit : I've tried his setup, worked first time to get in, took me like 10 try to get out.

I can get in reliably, and usually out of the building on my first try. I'm not sure how to explain the positioning for leaving, but the fast way doesn't have to do with lining the dot up to the door. Also, thanks for correcting the name of the skip, I joined the discord since I plan on running this game a bit :) there is another glitch at the door where Seamus takes you after The Slums 2, hop on the chair and position towards the door. For a frame or two an "A" will appear just in front of the door, and if you hit A when it is available, you will jump right under the door. If you have completed the apartment glitch and have beaten The Slums 2 for the first time (before the reset), this area will be loaded and you can meet Seamus on the other side. I am still looking for a way through the gate that Seamus unlocks after bailing on you, if anybody finds a feasible way through then there won't be a need to play The Slums 2 for a second time, saving a few minutes