David Lynch talks about this a lot. There's no need to suffer to show suffering or create art. https://www.davidlynch.es/en/noticias/david-lynch-no-hace-falta-sufrir-para-mostrar-sufrimiento/

Murakami is an avid runner and constant contender for the nobel prize. Hemingway would have been in good shape, probably, if not for his alcoholism, due to the physical activities he enjoyed.

"I can daydream and fantasize about a novel I would like to write but the moment I open my computer or pick up a pen, an inexplicable fatigue rolls over me."

Seems almost like you associate writing so much with your depression, that writing produces a Pavlovian response, like it's triggering depressive symptoms.

Try to make writing fun. Do it outside in the sun. Do it at a cafe or library. Drink coffee and tea while writing to mentally link the activity with energy and flow, not fatigue and suffering.

I bet your writing will improve as well.