This issue happened to a friend of mine, and with his permission, I am inquiring on his behalf here.
He encountered a strange issue. When he started the game on Steam, it stays at the launch window, and after a few seconds, the window automatically closes. However, when he opened the game directory and clicked on RealRTCW.x64.exe to launch the game, it was able to start the game normally.
The game files for RealRTCW and Return to Castle Wolfenstein have not been changed, the integrity of the tow games' file has been verified and the game startup option has no additional parameters. In addition, Return to Castle Wolfenstein can be launched and run normally through Steam.
Here is his PC Information:
system: Windows 11 23H2 64bit system
CPU: Intel i5-10300H @2.50Ghz
Graphics: Nvidia GTX 1650
RAM: 16GB

When this issue occured, rtcwconsole.log ultimately stays at the following content:
...
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Try loading dll file E:\steamnew\steamapps\common\RealRTCW\main\ui_sp_x64.dll
Loading DLL file: E:\steamnew\steamapps\common\RealRTCW\main\ui_sp_x64.dll
Sys_LoadGameDll(E:\steamnew\steamapps\common\RealRTCW\main\ui_sp_x64.dll) found vmMain function at 00007FFC90600A40
Parsing menu file: ui/main.menu
This may seem like an issue with the .menu file, but as I mentioned earlier, it's not like that. This question is very strange and bizarre.

Check the firewall/antivirus exceptions for launcher.x64.exe

Check the firewall/antivirus exceptions for launcher.x64.exe
He added it to whitelist, but the situation remains the same, even after turning off firewalls and antivirus software.

Might be VC 2019 Redist issue. I suggest to reinstall it. It required for launcher to work. Usually being installed on 1st launch but you can do it manualy too.

Thank you, I will pass on the message to him.

Might be VC 2019 Redist issue. I suggest to reinstall it. It required for launcher to work. Usually being installed on 1st launch but you can do it manualy too.
He had installed the latest version Microsoft Visual C++ 2015-2022 Redistributable x86 / x64, but this issue still occurs.
Additionally, although it was previously discovered that click on RealRTCW.x64.exe can start the game and play the vanilla levels, a crash will occur when launched addon.
So weird it is!

Did you ever find a solution? I haven't played RealRTCW in a while and am now experiencing the same thing you are, I can launch it find by running the exe but not through Steam

Did you ever find a solution? I haven't played RealRTCW in a while and am now experiencing the same thing you are, I can launch it find by running the exe but not through Steam
I'm sorry, as this issue occurred on a computer belongs to one of my Steam friends, I am unable to reproduce it or attempt to find a solution on my own device.