Some days I literally can't string a sentence together - the brain fog gets that bad. I do write *something* every day - I need to, as much as I need to eat, sleep, breathe. But that 'something' mioght be just one, barely coherent, sentence.
Writing online content every day is not something I can do without damaging my mental health further. I've learned it's best to celebrate what I can do, instead of mentally beating myself up for what I can't. It's like criticising myself for breathing the wrong way - it's ridiculous and it doesn't help.
But everyone's different, and what works for you is always what matters :)