Is it possible to install it?

Yes, it is, I'm playing it right now. Let me first explain something: the "Mac" version of Fallout sold here is actually the Windows version wrapped in Wine, a compatibility layer for running Windows programs on Unix-like systems (of which macOS is one).

OK, with that out of the way, here it is: download Fixt and Fallout first, expand the mod if necessary. You should have an EXE file for the mod, that's the installer. Now right-click on Fallout.app in the Finder -> Show Package contents. You are now inside the app bundle (an app is really just a directory with a specific directory-structure). I'm not sure about the patch you have to take, I think it was Contents -> Resources -> game. There you will see another Fallout.app, right-click and Show Package Contents again. There you will find an app called Wineskin.app, launch it.

Wineskin is what is used to manage the Wine installation that is bundled with the game. You now want to "Install Software" -> "Choose Setup Executable" and from there follow the instructions like Windows users as well. When you are asked for the path to install make sure you pick where Fallout is installed to (C:\GOG Games\Fallout" in my case. The installer will think that the insides of the wrapper are a hard drive called "C", that's normal.

If you are wondering why the game is wrapped up twice, my guess would be that it's because of GOG Galaxy. I don't use Galaxy so I just take the inner app (the one with Wineskin.app) and throw the outer one away. The mod installation procedure I have outlined above applies to pretty much every mod out there as well.

This doesn't work on Monterey. I'm guessing you can only do it on 16 bit MacOS.