I can't put my hand on my heart a swear Mandy is a dude, but I think they could very well be. They could also be a troon, or fat chick, or any number of other things. They are not who they claim to be though.
It's true, fat chicks catfish, but what fat chick catfish hides their voice? Even if you can literally hear how the fat folds are compressing her lungs, she would still get tons of positive attention and thirsty guys in such a male-dominated community as TF2 or the lawsplaining fandom. And that is assuming she has giga-fatvoice.
If she had an illness that fucked up her voice, she would say so. In fact, it would have been
the play. Troons and catfishes have been using the "oh no guise my mic broke teehee" move since the dawn of VOIP. And it gets really
transparent after your mic has been broken/glitching/muh drivers for a month, let alone the years that this person has been operational. The illness gambit wouldn't even be a lie if he's a troon, since they consider their maleness to be a disease. It would only get awkward when half the server is claiming to be a female with an unknown illness that targets their vocal chords.
Mann-D (I am adding the extra n to mann because he will appreciate the TF2 reference) is a man. The odds that he's a tech-savvy fat chick who catfishes with pics of big titty goth babes that have been edited to prevent discovery, but is also so socially anxious that she pretends her mic is permanently broken is simply too improbable.
The only reason I don't say impossible is that Mann-D plays Mann vs Machine (MvM) which is the PvE mode of TF2.

If he were a PvP Scout & Soldier, then he'd be the average Adderall-popping troon in thigh-highs that plays this game. Whereas PvE might be more the socially anxious fat chick's speed. Of course, having Bonnie Rabbot right there offsets my personal doubts. We all know the ironclad Sonic -> autism -> troon link.

