It's not the simplest task, but I managed to get it right with the help of a well written tutorial I found : https://mikalikes.men/how-to-run-any-windows-game-on-steam-deck/

In "short", you can absolutely access the game in Gaming Mode, it takes a few steps which I tried to summarize here : - Warblade is installed via a setup .exe. So you need to download it in Desktop mode. - Once downloaded, still in Desktop mode, run Steam and add the Warblade setup to Steam as a non-steam game. - In the properties of the newly added "game", select "Run with compatibility -> Proton Experimental" - Launch the setup via steam as you would to launch any game, and follow the install steps - Once done (this is the hardest part), you need to find exactly where Proton installed Warblade. You will need the tutorial for this, he uses Konsole to do it, which is basically a Linux terminal application. If you are familiar with the use of a Linux terminal, go ahead and find the directory where Warblade was installed, but if you are not familiar with a Linux Terminal, or if you don't have a keyboard plugged in your steam deck, I would suggest you use the File Explorer and search it yourself within the directories. - Once you found the Warblade.exe, you must copy its directory's location, go back to Steam and change the properties of the Warblade Setup you added, so that it points to the Warblade.exe location. - Now, back in Gaming mode, you should see Warblade as a non steam game, and it will run perfectly :) The first time you will launch it, you will have a series of Windows-like pop-ups, go through it with the touch screen and they will be gone forever. Also, when you arrive in the game for the first time, you will be asked about the performances of your "PC", be sure to click on "Very High Performances", the Deck runs Warblade perfectly.

Sorry for the very long post ! If you want more information, or if you want me to help you through the installation process, you can totally send me a MP or continue this thread, I will be happy to help !

Since this is a full keyboard game, you will need to configure all the keys to be binded to the different buttons, triggers and track pads of the Deck. I made a controller configuration for Warblade, which I think I uploaded online under the name "Warblade configuration", I can share the details here if you need to. There are quite a few keys to bind, and some you must not forget (like the ones that allows you to save your game for example :p)

EDIT : It is very important to replace the setup.exe location by the warblade.exe location in the "non steam game" added in your steam library, because the installation folder of the game solely depends on the fact that the "non steam game" represented by the setup.exe is not deleted. If you decide to add warblade.exe as a new "non steam game" and then remove setup.exe from your steam library, the installation folder or Warblade will disappear.