You don't really mention which part of an IoT solution? An actual device in people's homes? On factory floors? Some kind of router or edge gateway? Backend comp

You don't really mention which part of an IoT solution? An actual device in people's homes? On factory floors? Some kind of router or edge gateway? Backend components? The component itself will already limit your amount of reasonable choices for a language or framework. You probably neither want to Java on a microcontroller with 256kB RAM, nor C on a backend.