I really recommend giving a read to atomic habits, I found it very helpful being someone who gives up on just about anything rather quickly myself.
But in essence what has helped me is tracking and starting small, like *really* small if needed. It used to try to change my life overnight and start doing like 5 new positive habits and burn out very quickly, realized that for most people that's just a bad a idea, even more if you are depressed in the first place. I would recommend thinking of something you want, having an end goal is ok but focus on the process itself.
IE "I want to be in shape -> I want to live as /be someone who cares about his fitness -> someone who cares about fitness will spare a bit of effort for it regularly."
So clearly I can't become fit overnight, nor can I become disciplined that easily either, so what I can do is start behaviors that such a person would have and that would lead me to closer to being that person. Which can mean starting with even 5 minutes of exercise a day. Maybe some days you will feel like doing more, maybe some days I will do the absolute minimum just so I can keep the streak (this is where tracking really helps). And eventually overtime it gets a tiny bit earlier, takes less mental effort and motivation and with that it's easier to work harder too. But the focus should be on doing at least the bare minimum but on a consistent basis and build up from there.
Another factor talked about on the book is environment. If you have easy access to junk food, entertainment etc then you will naturally and inevitable go there, and not doing so will take a lot of effort every time, so instead of having the willpower of not eating or playing a game each time you pass by them, making the things you want to do more visible and convenient and the things you don't want to more inconvenient and less exposed.
It really is almost impossible to do 180 changes, it's slow and frustrating but personally it's the only way I've been able to stick with healthier habits. Make them small, easy, simple. Give them time to become part of your life and only then think of what next little change you can add next until eventually your day is looking more and more like that which you want.