Extra steps to get cutscenes to function:

1. Download the zip file from https://gitlab.com/steevyp/mf-installcab_steamdeck a) Navigate to the "Code" button in blue b) select the zip file [or any of the other files if you see fit] and downlaod c) I saved the file in my Downloads Folder
2. Extract the zip into the Downloads folder
3. Within the mf-installcab_steamdeck-main, right click and open a terminal window [this will load up the location you are visually in inside of the terminal environment.
4. Within the Terminal copy and paste this command: PROTON="$HOME/.steam/root/steamapps/common/Proton 8.0" WINEPREFIX="$HOME/.steam/root/steamapps/compatdata/462780/pfx" ./install-mf-64.sh -proton

Information provided by user: CommandCraxX a) As a Mint user, you will need to instally Python 3 [within the terminal, run sudo "apt install python3" without the quotes] b) Install cabextract [within the terminal, run "sudo apt install cabextract" [without the quotes] c) open the install-mf-64.sh file with whatever editor you want. [in my case, I just used notepadqq] and change the Python name to Python3. There are 6 instances that need this change. [example: python > python3] That's it. Save the changes.

5. Once the command completes, note the very last line shown within the Terminal. "Now you need to get mfplat.dll in your application directory"
6. From within the "mf-installcab_steamdeck-main" folder located in the Download directory, copy the mfplat.dll file
7. Within Steam, navigate to the Darksiders Warmastered Edition game and select the "manage" icon. Looks like a gear. Select Manage > Browse Local Files. This can be done by right clicking the game name on the left tool bar as well.
8. Paste the mfplat.dll stated above from step 6
9. From the gear icon or right clicking the game title, select "Properties
10. Navigate to "Compatibility" located on the left columb
11. Check the "Force the use of a specific Steam Play campatibility tool
12. Select Proton 8.0-X [or whatever the most recent version of Proton 8 is available]
13. Close this window
14. Restart Steam [honestly, I'm not sure if this is a necessary step, but I did it as a precausion]

In Game cutscenes should now play properly.

I want to thank everyone below this post for pointing me in the right direction. I created this instructional for those of us who are less familiar with Linux, such as myself.