You'll need to have beaten the game atleast once, as this will allow you access to the "developer commentary" feature.

To enable developer commentary, you'll see an option to do so In the difficulty selection when you click new game.

The developer commentaries are these speech bubble thingies you find throughout the game.

To put the exploit in effect, you'll need to interact with one of the developer commentaries. I'd recommend going for the one in the starting area of the game (just before the tunnel where you see the shadowy figure, picture below), as this will prove very helpful for a later step.

MAKE SURE YOU EITHER HAVE SIMON'S PHONE ALREADY EQUIPPED OR PUT IN ONE OF THE QUICK SLOTS !!!!!

As the developer commentary is playing, you'll need to switch to Simon's phone and call 911 (or 122), which will play strange audio from the phone. You'll notice that you are now able to move freely while the developer commentary is still playing.

VERY IMPORTANT. Do not let the developer commentary conclude. If the commentary concludes, you will never be able to do the exploit on that file again.

Instead, get to the end of the room as fast as you can and enter the next area. It's possible the commentary will cut out before you get to the next room, but as long as it doesn't end normally you'll be fine.

This will send the game into a state where it thinks you're still listening to the developer commentary, although you can continue the game as normal.

And that's it!! Simon will no longer be able to take damage from enemies. This exploit is very useful if you find yourself unable to beat the game by normal means.

Note: It is still possible for Simon to die in some scenarios. For instance, the first boss in the game (Sawer), is able to kill simon, as his attack transitions into an instant death animation, rather than JUST an attack. Simon can also be killed by Taller, moving trains, crushing, falling into pits and other instant deaths which happen in cutscenes (The train falling and Dr. Purnell shooting you when you walk up to him during his boss fight).

It is also important to note that pressing ENTER at any point of gameplay will disable the exploit permanently for that file. Pressing ENTER to skip cutscenes won't effect the exploit.

I hope you find this exploit useful, or fun if that's what you intend to use it for. Please let me know if this is already known about in the community, I found this exploit on my own by accident and I would love to know if it has already been discovered.

Thanks for reading!!