A lot can be learnt, as I did for decades. Always obsessed to try all the various methods, and enough of them work for me, to a degree.
But I think when it has gone to the point, there is more to it. In my case, it was the ADHD. My brain did not follow through with the plan to start doing the task, always had to push through some inner “pain”, and that is not pleasant. For others, it might be depression. So I had a lot of pain just to do the highest priorities barely good enough, while a normal brain would do it all without the effort, and kick in sweet dopamine rewards after each task.
Yes, the anxiety, guilt, pressure that gets it done eventually in a panic frenzy, when the adrenaline kicks in. It was not a good life, though.
For my son, I don’t want that, I want to be understanding that he might have a dopamine/noradrenaline imbalance that would make it disproportionately cruel to force him to clean his room right now. (He’s getting checked, of course, but in the meantime got to take my best guess.)
But the result is that he does not get even priority tasks done, sometimes.
I’m sure I can find a different way for him, starting with getting him checked. Some methods also work for him. E. g.: Don’t have to do it right now, but when it’s 5 p.m. / the video is done / whatever, set a stopwatch and do 10 minutes of cleaning. Or, since he can’t find where to start, do one thing: All garbage into a bag, or all toys into the box, or all dirty clothes into the wash.
Don’t get your anxiety back, find a different way for yourself.