Question is in the title. How?

is the pause skip: clicking with the mouse to pause at perfect frame timing when the ending cutscene starts (you can see how he hovers mouse on the pause button on these instances), you can basicaly get the pause menu during the cutscene, which allows him to "exit the game" during this cutscene without having to do the glitch entering the game (not appreciable because of how fast he is, but you can see the menu on this video)

this realy can be done at any minigame, and is essentialy the fastest way to get a cutscene skip, but generaly runners wont do it in most of the minigames because of how precise and inconsistent it can be; tho it is necesary to execute in at least 1 minigame (either climbing or table tennis) to get skip in the maximum amount of minigames

So it's a frame perfect click? Seems like hell but might try to pull it off

im quite sure is frame perfect yea, releasing the click at the frame entering the cutscene

you can hold the click before and just time the release instead of clicking at the moment, that helps with the timing

I've been practicing it and it seems a bit too easy to be frame perfect, I think its a two or three frame input. I also did it once right before the cutscene started, and got a black screen while in the menu, but still got credit for the scroll and was able to warp out