XCOM relies on older Microsoft Visual C++ libraries. If you are missing the 2010 or 2012 versions, the game will not launch.
Read this first: This solves 90% of launch failures on Windows 11. xcom: enemy unknown not launching windows 11
: Manually run the installers found in the game’s _CommonRedist folder within your Steam installation directory. Reset Configuration Files XCOM relies on older Microsoft Visual C++ libraries
If a file has been corrupted or a Windows update altered a permission, Steam can repair it automatically. Steam can repair it automatically.