If you need one for the original reason they where introduced ie a hidden disability, then yes, but as for mask exemption then that will vary. I didn't think it allows you to get around the US requirement to wear a mask on US inbound/outbound aircraft on its own though. The company I work for will not allow people to be excused from wearing a mask just because they have a flowery lanyard on, we need a letter signed by a medical practitioner supplied in advance for that to happen. (The letter does not need to say what the medical condition is, just that they should be exempt for medical reasons)