When I first started playing this game, it loaded up in a very small window. I then tried to make it run in full-screen by pressing Alt+Enter and it worked well except the game was still in 4:3. Assuming I could get it to run in 16:9, and since the main menu suggests it, I tried pressing F5 and F6 to see what it would do. And it actually made things worse.

The game now looked like this on my monitor and no matter how much I pressed F5 or F6, it wouldn't go back to its previous and correct configuration :

As it turns out, there's no way to run this game in 16:9. It was made to run in 4:3. But, quite frankly, you shouldn't let that technicality deter you from playing it as it is a pretty cool experience.

In order to fix any issue you might have when trying to run Always Sometimes Monsters in all its 4:3 full-screen glory, you need to do the following :

1) Locate the file "Game.ini" in the installation folder of the game.

The exact location of your Steam folder may vary, depending on where you installed it on your computer. On Windows, by default it should be in "C:\Program Files (x86)\" but then again, maybe you chose to put it somewhere else (Different drive, different folder...).

Once you've located it follow this path to find the file "Game.ini" :
"Steam\SteamApps\common\Always Sometimes Monsters"

2) Edit the file "Game.ini" with Notepad

Open the file "Game.ini" by right clicking it and then choosing to open it with Notepad.

In Notepad, edit these three lines under the category "[ASM-Screen]" :
[ASM-Screen]
Fullscreen=1
FullscreenRatio=0
WindowedRatio=1

Once done, save and close the file.

3) Making sure these parameters stay that way

After closing the file "Game.ini", right-click it again and choose "Properties". This will open a new window on the bottom of which you will find the attributes of the file "Game.ini". Check the "Read-only" box then click on "Apply" and "OK". This will ensure no further modifications can be made on this file by either the game or yourself. If you ever need to modify that file again, just go back and uncheck that "Read-only" box.

That's it. Now Always Sometimes Monsters will always run in full-screen when you launch it.

As I mentioned earlier, there doesn't seem to be any workaround to make the game run in 16:9, whether in full screen nor windowed as I am writing this.

If by any chance, I'm being mistaken and you know how to make Always Sometimes Monsters run 16:9, leave a comment and I might add it to this guide.

Everything described in this guide was gathered from this Steam Community post:

https://gtm.steamproxy.vip/app/274310/discussions/0/34095131782260187/

Special thanks to the Steam users who contributed to this post, as this guide wouldn't exist without them.