You can play Alan Wake 2 on the Steam Deck in a couple of ways, one includes the Heroic Games launcher and a few driver tweaks and the other is via GeForce NOW.
Running it locally on the Steam Deck leaves a lot to be desired though.
Video Guide
Text Guide
1 - Change the Steam Deck UMA Buffer to 256M. To access the Steam Deck bios settings you need to power off the Steam Deck, then power the Steam Deck on while holding the Volume up button. When you hear the Deck boot sound, keep holding the volume up button but let get of the power button and you should see a screen like below.
2 - Go into the Setup Utility Option
3 - Select Advanced
4 - Set the UMA buffer to 256M
5 - Save and exit using the button on the left of the Steam Deck next to the D-Pad
6 - Start the deck and enter Desktop Mode
7 - Search and Install Heroic Game Launcher in the Discovery Store
8 - Login to your Epic Games Account in the Heroic Games Launcher or log out and back in if your library doesn't update
9 - Install Alan Wake 2 from the library in the Heroic Games Launcher
10 - From the Settings menu on the Alan Wake 2 Game page access WineTricks
11 - Select the Default Winprefix and select ok.
12 - Select Install a Windows DLL or component and click ok
13 - Select d3dcompiler_43, d3dcompiler_47 and vcrun2022, then click OK - There may be some warning pop ups during the install, just click ok to dismiss them. Once the installation is complete. The winetricks window will appear again, you can cancel out of all of the screens.
14 - Add Alan Wake 2 to Steam using the 3 dots in the top right of the game page and select Add to Steam
15 - Now you can return to Game Mode and launch Alan Wake 2 from your Non-Steam section of your library and you are good to go.