how do people with depression in the harry potter universe perform the patronus charm? asking for a friend

Maybe it’s a matter of perspective. Like, sure, people with depression can’t perform the patronus charm but they’re also less affected by dementors in general: Oh your presence makes everyone feel shitty and you steal away my happy memories? Well guess what, I already feel shitty and can hardly remember what it was like being happy. So guess who’s the loser now!

Probably people with functioning depression can last longer when faced with a dementor, so they do have more time to scrounge up any happy memory for patronus charm. And, perhaps, instead of a full blown guardian animal all they get is silvery wisps, but maybe that will be enough to fend off the dementors for your non-depressed friends to whip out their glowing capybara of happiness.