Remove dust build up from the port. A very thin piece of plastic cut to a long triangle is a perfect tool for getting things out of there. I use the plactic from grape containers. It's thin but still hols it's form when cut into strips. I do it every so many months. It's amazing how much debris builds up in there. Also if you haven't already tried a different cable do that. I had a problem with this and it turn out the cable I had was bad.
For me it went away - but only for a day or two. I'm gonna take the S21 to the store for a warranty repair.
Seems to me like the phone is waterproof (IP68) but you cannot charge or otherwise use the USB-port afterwards.