Thanks. Restart the phone a few times.
Consider using another cable and / or hdmi adapter ( if any). Check the equipment you're connecting too as well. Try connecting to another USB device such as a PC and check if issue is still occurring.
If you're happy, the cable, etc, is good, then you could try in Safe mode to rule out any 3rd party app or customisation interference
To get to Safe Mode - Long press Power button, long press Power off icon, tap Safe mode icon. (When booted into Safe mode, you may need to turn off flight mode as it sometimes enables itself). Monitor your devices behaviour. If the issue is fixed, then you know it's one of your 3rd party apps or customisations that were the culprit. It's then up to you to determine which one by a process of elimination.
Try a partition cache wipe
Plug into a working PC or laptop or other Samsung device
https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/Failing that, then consider the nuclear option, a full factory reset. Backup first.
If it is still not working, then maybe there's a problem with your USB port (even though charging ok). Check the port with a torch and look for build-up of dirt or debris. Blow it out. Don't attempt to poke any metal objects in there.
There's also a diagnostic you can use via your Samsung members app. Head to the Support section and run the USB diagnostic test.
