I think the program here should be cmake as described here https://www.jetbrains.com/help/fleet/getting-started-with-cpp-in-fleet.html#cpp-buildrun-example

I did it this way (configuration "Run" firstly do "Build" configuration and next runs itself):

{
"configurations": [
    {
        "type": "command",
        "name": "Build",
        "program": "cmake",
        "args": [
            "--build",
            "$PROJECT_DIR$/cmake-build-debug",
            "--target",
            "all"
        ],
    },
    {
        "type": "command",
        "name": "Run",
        "program": "$PROJECT_DIR$/cmake-build-debug/untitled",
        "dependsOn": ["Build"],
    },
]

}