@diobolical OK, 2 things to do for further troubleshooting:
Go to your Steam SCFA folder > DirectX, then run the DXSETUP.exe installer to re-install the DirectX files that SCFA uses (just in case those weren't installed correctly). Go to Steam > Library > right-click SCFA > Properties > General > Launch Options > copy/paste this into that field:/log "A:\SteamLibrary\steamapps\common\Supreme Commander Forged Alliance\logs\steamfa.log"
I grabbed that file path from your client.log, so you'll need to change it if that's not the correct path to your Steam SCFA install.
Try Steam SCFA again after doing the above.