If you search for “how to clean usb-c port” or similar you’ll find a lot of suggestions.
I’d recommend you start by carefully using a vacuum cleaner with a narrow tool. Some people recommend using compressed air cans. But where does the dirt go, eh? Sure, some of it comes out, but a lot goes further in
My 5p’s worth : USB-C port unfortunately, much like the very common USB micro-B, includes a very thin “tongue” which carries the circuit contacts.
This to my mind is much less good design than Apple’s Lightning port, which is really robust and easy to clean. I think the best design solution I’ve seen. Frankly I can’t understand why the industry didn’t negotiate a means of adopting Apple’s ideas - well doubtless money, as usual. Maybe there’s a technical reason too. But the fact is that USB-C is more fragile and allows little room for cleaning, while affording ample scope for the dirt to accumulate. @amoun 's idea is good - if you can be bothered to remove the case for each charge. Or put a bit of adhesive tape on the outside of the case to cover the hole. But for cleaning, use great care not to damage that thin piece inside the port!