Why does my phone show moisture detected warning though it is dry

the moisture detection shows up if the port and/or the cable is dirty or just corroded enough that they don't quite give the expected amount of power.

Try cleaning the port with a toothbrush and some isopropyl alcohol. If you have a magnifying glass and a good lightsource you might even be able to see your problem

And if that does not help. You might need to replace the port by yourself or using a repair shop.

Ps. Some people claim that they bypassed the warning by plugging it in, then force restarting the phone. (Power button + volume down) but only you can confirm if that does the trick.

Good luck (⁠•⁠‿⁠•⁠)