The compiler has optimized the rendering engine too much to be decompiled into any useable code. Somebody is working on Linux and 64bit support which will need to have this completely rewritten. github.com/dkfans/…/bflib_render_gpoly.c
The maintainer of KeeperFX told me that EA does not have the original code anymore though.
Playing modern Windows games on Linux and SteamOS is done using Wine and Proton. Wine is available on almost every Linux distro and Proton comes* with Steam.
*You can use Proton outside of Steam but it’s quite hacky and not really needed.