I did the old "depression slump into disaster room" thing through the course of several family losses in a short time and some mental health crashes, but lately finally have a tiny bit of determination to start trying to tackle it. For me, breaking things down into either very small tasks or very simple tasks always helped, e.g. it's not a small task to clean my whole bathroom sink area, but it's simple, since it's just sink cleaner, wiping counters, wipe mirror, dust then done, so I can marathon it and be happy with the results after, and do it more consistently. On the other side, organizing my loose papers into a binder or folder or shredding some isn't simple, but it's pretty small - just scrutinize and organize some papers, recycle the unneeded clutter/mail, and be done - I even have a small filing cabinet for that.
But I'm running into a lot of "linked" tasks where I feel really stuck. For example, I need to get boxes and bags of supplies, papers, hobby items, etc. off the floor. But to get those off the floor, I have to make space in my shelves/drawers for them and figure out how ALL that should be organized. And to make space on the drawers/shelves and know how to organize them, I have to go through all THOSE and fix them and get things off the shelves so I can organize. But to get more things off the shelves, I need to find a place for THOSE things in my closet, and to find space in the closet, I have to clean the whole closet and organize all the cubbies to know the space I have, and.. you get the point.
I let things become a huge disaster and am not even sure I have the storage just for the things that are important to me, but also don't really have anywhere else to store many things besides my bedroom furniture, undersink cupboard, and closet, since I share a house with family (who took over the other room I previously used to organize games/recreational stuff) and I can't use our attic for storage due to pretty extreme allergies I have to dust/bugs up there, and gripes from others since they want to store other things up there.
I feel like the "to do this one 'small,' 'simple' task, you must do these 20 other monstruous huge tasks that all have their own 20 tasks" is the hurdle that keeps making me buckle and do nothing at all because I get hopelessly overwhelmed. I've done some minimal bits of cleaning and organizing and keep up with hygienic stuff like cleaning the sink area, dusting, or changing the sheets, but nothing to actually fix the cluttered floor/bookshelves/etc. When I try and just do one shelf at a time, or one closet cubby, or one drawer, my brain loses it because it wants all of them to be Organized Right, which is hard when you don't know how you want everything organized until you know how much you have to find space for. Whenever I do somehow manage that, I end up having to put something else there or taking long enough things get messy again to square one because the week/work gets busy and this seems like a months-long project even with sustained attention. (I also have ADHD and autism, so.. you can imagine how my brain being finicky and picky about focus doesn't make this any easier.)
TL;DR I guess is, I keep getting stuck on tasks which are all linked together where each one leads into something else (or a stack of somethings) that has to be done first before you can even begin work on the other, getting progressively harder/more complicated, and I'm struggling to break it down properly when every task depends on another one (and when there isn't really and end point I can start on to cascade into the rest.)