Not much to add but re-emphasizing the usual: small things add up. I know it's cliche but it's cliche for a reason: diet and exercise (again, tiny changes are realistic and attainable and sustainable) go a long way in the medium term.

See yourself not as a failure but as someone who has been caught in a self-fulfilling feedback loop. You have much greater potential than your current existence, you yourself have said how you were once more functional. If it took you years to get here, it might take a long time to build new habits. As long as you can maintain the will to change, cherish the small victories and don't give up when you have hiccups or speed bumps or back slides or even nose dives if they happen, as long as you keep trying, eventually your will will reach a critical mass, reverse the inertia, and you will slowly find yourself in a position you can be more proud of. Be patient with yourself, it is not antithetical to being firm or disciplined. Your desire for change shows you are already in a better frame of mind and will have better success than most.

Trust me, my life ate total shit in 2022-2023, I'm only barely starting to see the results of attempt and re-attempt and re-re-re-re-attempt to stop the death spiral. Do not let the fog make you blind to a better future you can slowly build, the fog and its lies about you are not truth, they are delusion.

Also, some minor radical change goes a long way in tandem with small victories. Like, I don't know, I once took 4 days where I didn't speak to anyone and refused to use technology, I basically just writhed inside my head the entire time, but it was a good thing, fuck the internet. Same thing with sobriety.

Best of luck comrade.