The advice in articles about decluttering is always to do it in small chunks, so you don’t get overwhelmed by it. A drawer or cupboard at a time.
I’m not great at that, as I probably have ADD, so procrastinate until I have a deadline such as a decorator starting in two days and then have no choice but to work round the clock, but we’re all different, and that advice seems sensible if you can do it. Another idea is to set a timer and do as much as you can in ten minutes- you can do that for ten minutes every hour, or every day, depending on what works for you.
I have managed to get most of the house done over the past couple of years, and am now working on keeping it uncluttered. I never leave a room without looking for something to take with me to put in a bin or put away, try not to leave things on the stairs, but just take them and put them in bedrooms straight away and so on. Very basic things that most people do as a matter of course.
I have a couple of rooms still to do, but having the rest of the house finished is an incentive - it’s so much nicer to be able to put things in cupboards that aren’t groaning with ‘stuff’. I’m never going to be Marie Kondo (and I don’t want to be) but it’s never too late to learn, and small changes can make a big difference.