Hi, I just had a similar issue even if with a different laptop. The USB-C are a real mess, what you need is a USB-C cable that supports alternate mode and display port with 4k@60Hz support, as you are able to get 4K @ 30Hz the one you have should work just fine. Then what you have to do is opening Settings > External device manager > Input signal plus and chose USB-C Frankly speaking I have no idea why Samsung went for this super weird solution but this is how I fixed it. I hope it helps.
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