While a headphone is connected, the proximity sensor is completely ignored during calls. This means that the screen will not turn itself off nor ignore accidental touches. This happens whether a headphone is connected via 3.5mm jack, a USB-C -> 3.5mm adapter, or Bluetooth. This also happens across different pairs of headphones. Can anyone confirm whether this is happening on their device? ASUS, please fix this. This is a major problem.
Somewhat related, I've found the proximity sensor to be extremely buggy without headphones (holding phone to head). Constantly knock the mute button and if I try to use the phone during a call (while on speaker), the screen turns off (proximity sensor activation).