How they do that? (Glitch Alien Isolation)

They talk about a tool you download to "freecam teleport" through a door.

Adam says that they use a software. But if you are asking what it's name is, I don't know.

So some info:

• FPS effects on Half Life 1 for example: https://wiki.sourceruns.org/wiki/FPS_Effects
• AGDQ run where they talk about the FPS limitation and (wanting) to use it : https://youtu.be/dMmsD3FTrjU?t=1386
• Speculations about using Fraps or " FPSLimiter 0.2 " https://encodingtalk.com/threads/use-fraps-as-a-fps-limiter.141/ (posts are from 2011)
• Found some A. Isolation forums where they discuss FPS limiting and "Certain clips are only possible at extremely low FPS " part.
  https://www.speedrun.com/ai/thread/nio77/1#h6wys

Seems like the word you're looking for is "FPS toggle" , likely you can find more options and ideas on various speedrunner forums / communities