Huh. The same thing is happening to my mom's S9 Plus right now. She's quite clumsy with her phone and left it in a wet bag for a fair while - exact same story as yours. Came back to charge afterwards, first the fast charging wouldn't work, then it stopped charging through wired charging altogether.
Thankfully we had warranty (extended) on it so we've since filed a claim, paid a deductible and am now waiting to reset the phone to factory settings and ship it off to Samsung.
I'm no expert in the electronics field - and I'm sure others in this thread could explain the science much better than I can, but essentially water and electricity are still a terrible combination, no matter how "water-resistant" a phone is. Your electronics are always susceptible to damage by moisture/water regardless of an IP rating, and it sounds like to me your phone was caught on the short end of the stick. Your phone sounds like it's suffered some internal water damage.
It looks like you're going to have to get it fixed, if not at the very least checked by a professional.
This happened to my s10 when i had one before switching to apple! What actually fixed it was factory resetting it believe it or not it actually worked again
side note: use common sense when doing that .