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.
On Linux I managed to disable the motherboard’s Bluetooth because it showed up as a usb device and then I’m able to use a dongle just fine.