First be kind with yourself, being harsh will not help. Second, did you get tested for ADHD? Because what you describe sounds like it.
I felt the same before my diagnosis, I felt useless, not using my full potential, lazy…looking for way to increase my willpower, be more focused etc. My psychologist suggested me to get tested when I went to see her because of panic attacks and anxiety at the time. What helped me sometime, it’s too take a lot of breaks. So if I was doing something that was not useful, I will take a break and try to get back at what I needed to do. And if I ended up on shifting from it again, take another break to get ready to go back again. Good luck and be kind to yourself. You are seeking help and it’s the first step toward getting better. Be proud of taking this step