This is a bit involved, and has a bunch of stuff to be done on the terminal, in desktop mode. It's possible that playing later would be possible in deck ("big picture") mode as well, but I can't confirm it for reasons of not using a deck myself. I did get integrated mode working on linux though.
Make sure you've installed the game, verified it's integrity, and have launched it at least once after that. The following instructions uses non-flatpak Steam. I don't know where flatpak installations of Steam keep the user data, and modding involves quite a bit of manipulation of folders. You may be able to adapt this guide to flatpak with looking up where those paths are on the distribution of linux that you're using.
Use the browser to download the Oracle JDK version 25. You want the Windows version, use either of the installers (not the "compressed archive" one). Site will probably put you to Linux tab, be sure to use the Windows one. https://www.oracl