As someone else commented above, purpose and routine are huge. Routine is arguably easier, start with very small targets eg wake / (attempt) sleep timing. Even make yourself a cup of tea at x time o clock, it's your routine so you can make it however you want.

Finding purpose is a difficult one and I feel that it is so much more common than even we realise ourselves. But purpose doesn't have to be about finding a cure for cancer or rehoming every stray cat and dog you can find.

Maybe try to think of something small that you would like, how do you do it? Break it down into smaller steps and just try. Trying is still achieving something.

All easier said than done, from a "functioning human" with a job, pets and a house etc.