What GPU upgrade makes sense with an i5-9400F and ASUS H310 motherboard?

The motherboard itself shouldn’t be the main limitation. A modern PCIe graphics card should work as long as your power supply has the required connectors and enough wattage. The more important details are your PSU model, monitor resolution, and target frame rate. An RTX 4060 would be a reasonable upgrade from the GTX 1660, though check current pricing before buying.

Before choosing a card, check whether the game is being limited by settings rather than just the GTX 1660. Black Myth: Wukong is demanding, so lowering ray tracing, using upscaling such as DLSS if available, and adjusting texture quality can help. If you want a clear upgrade without replacing the rest of the platform, look at current midrange options and compare them with similarly priced used cards.

Your i5-9400F can still handle a midrange GPU fairly well, particularly at 1440p where the graphics card does more of the work. I wouldn’t pair this system with a very high-end card because the CPU may limit performance in some games, but cards around the RTX 4060 class are a sensible match. Make sure the power supply is from a reputable brand and meets the card’s requirements.