Not sure if just trying more methods will help you, but here are some that happen to consistently work for me:

• Always work with a list.
• When everything seems overwhelming and I can't get myself to start, just pick ONE item from the list.
• If there is no list, just making the list will do. It may be empty. Done for now, enough, no need to start on it yet.
• Granular items.
  • Instead of "pack suitcase", break it down like "get suitcase out".
  • Split the task of "read X" and "understand X". That stops obstructive thoughts like "I wouldn't understand it anyway, and then I'd need to as ... but can't right now because ...".
• The only new breakthrough from this year: When even doing one item from the list feels like too much, only simulate doing them in your head: https://lemmy.ml/post/36147982
• I have a section of "structural improvements". Those are things that, once done, improve my life, forever. E. g. getting this diagnosis. Getting a dishwasher. Getting a maid. Unlike, for example, clean the kitchen, which is temporary.
• implementation intention: Might feel overwhelming to "stop browsing right now", but set a timer to stop in 5 minutes. Or "when the timer finishes, I'll do the simulations on list items".

Real habit building still does not work for me, though, even with a specialist therapist. That'd be the real deal.

Even f it only sticks for a week, that's one week that's way better than if you had done nothing. I say keep cycling through your methods, pick one that speaks to you (or pull one out of a hat every so often - gamling is fun when it doesn't impact your economy or relationships!) and then pick another when it wears off or even on a schedule like every month or so.

If this means you only manage any functional strategy one week per month, that's still twelve weeks of the year where your quality of life has improved compared to not (re)using any strategy. That's three whole months! Massive improvement!

The thing that seems to work most consistently for me is other people. I need to body double irl or by phone, but it can't be someone I live with because then the effect wears off and I get too comfortable having them around. Anything that becomes predictable and "routine" becomes ineffective, but social interaction is usually stressful enough to get me going and getting shit done.

Hyperfocus (short and intense unreachable to the world type attention, not the special interest long-term hyperfocus) is one other way, but that's not reliable at all. I need to get my set and setting completely right to be able to aim and maintain my hyperfocus on the right task, which is where I need.. body doubling. And it's not really long-term solution either since it's easy to burn out from, with the whole "forgetting to drink or pee or blink for 10 hours".