I battled with this for twenty years - I am one of nature's hoarders - and eventually hired somebody to help me. Not exaggerating when I say it has transformed my life. We did it gradually, a little bit like Marie Kondo - clothes, and then household textiles, and kitchen stuff, and books, and old electronics, and so on. It did mean making a bit of a mess day by day because we tried to get all of whatever type of thing together, and then I would decide how much of it I could realistically use/store and how much I would donate. Went through cupboard by cupboard.
Then she would take away everything that could be taken away to sell/donate, or she would help me list stuff on vinted etc., and if there were things that needed repairing she would take them for repair, and with old junk she was really helpful in nudging me to throw it out. She also helped refile all my bills and papers so that things are easier to find.
Then I was diagnosed with ADHD and have realised that actually I manage much better with ongoing regular support, so now I have someone who comes in every week, a bit like a cleaner but for filing, taking stuff to the tip/charity shop (I don't have a car) and just generally keeping on top of things.
It does cost money, but for instance with her help I've been able to clear a 'junk' spare room and and rent it out, and that way more than offsets the cost of her help week by week.
I know so well how hard it can be! I wish you all solidarity with getting to grips with this.