Medical reasons to my knowledge is defined rather limited. There's an exception but in doubt you have to show a doctor's note saying that you need to wear a mask, otherwise you could be forced to unmask. So if you choose to do preventative masking but aren't ill yourself this isn't technically allowed - this isn't widely enforced, but still something that wasn't thought quite through.
Medical reasons to my knowledge is defined rather limited. There's an exception but in doubt you have to show a doctor's note saying that you need to wear a mask, otherwise you could be forced to unmask. So if you choose to do preventative masking but aren't ill yourself this isn't technically allowed - this isn't widely enforced, but still something that wasn't thought quite through.