Since the Executable Standalone provides the quality as the full version of Enscape, it also requires the same System Requirements as seen here, including compatible NVIDIA / AMD graphics card with at least 4 GB of VRAM.
If these conditions are met, the reason for an Executable Standalone file not running is almost always an outdated graphics card driver.
In this case, please make sure your client updates their graphics card driver for the machine they want to run the Enscape Standalone Executable file on. This will drastically increase the chances of Enscape being able to run on that machine.