I was troubleshooting Bluetooth connection today and I thought that this is somehow related to software (PipeWire, bluez, bluetoothd and all that stuff). But no. Apparently Bluetooth barely works when WiFi antenna is disconnected from my ASUS motherboard.
Anyway, this might save a lot of time for someone, so I’m posting it here.
It would be a waste to give them separate antenna, they both operate on the same frequency (and often with the same radio, although the BT side of an m.2 card is often supported by usb instead of pcie)