Which component is responsible for the network connection on the mobil

When I am connected to the Wi-Fi network at home, my OnePlus 6t occasionally disconnects from the Wi-Fi network and the mobile network out of the blue for about 20 seconds and then logs back in automatically. If, on the other hand, I switch off Wi-Fi and connect to the internet via the mobile network, the connection has never been interrupted. I have already reset the phone and during the set-up process the same problem occurred again, so it must be the hardware. My question now is, which component do I need to replace? Where is the antenna for the connection to the WLAN/mobile network, is it a separate circuit board or is it on the motherboard? It would be nice if someone could take care of me, as the problem is really annoying, especially when the connection simply drops out during a phone call. Thank you in advance.