Jane's WWII Fighters was released way back in 1998. It is considered a good WWII Flight Sim in it's day. I still have my original CDs. I always felt that it has a good balance between Simulator and game. Have recently gotten the bug to play the game again, I set about getting the game running and looking as good as possible on modern hardware and operating system (Windows 10). For a video game that, as of this posting, is 22 years old, I think I managed to get the ol' gal looking pretty good!
Download the installer to a location on your Steam Deck and install it like you would any other Non-Steam Game. This video show the Steam Deck settings you need to apply after installing. Also if you have WWII Fighters already installed on your desktop PC, you can copy that install to the deck instead of doing a formal install.