Hi @damaj301damaj
Can you charge the phone OK using a USB-C charger?
Also try using the [https://www.samsung.com/uk/support/mobile-devices/how-do-i-use-the-voice-recorder/?srsltid=AfmBOopgHGob5SNs2KROJfoHrrPQGH3CfkNsLYjhjqKmzUPQ70acDdda|voice recorder app] (record in stereo) just to see if that works.
Trying to prove if the problem is related to the charge port board e.g. loose flex cable connection, as some of the antennas for the phone are located on this board
If the above work OK then it may be a systemboard problem. Here's the [document|40956] that may help.
Go to p.38 (of 55 pdf) to view the GSM, WCDMA, LTE troubleshooting flowcharts and check if it leads to where the problem may be.
There are board layout diagrams on p.2→p.5. Use the search function in your browser to find the location on the board(s) of the components mentioned in the flowchart. You have to zoom in a lot to see them.