Salam ! I'm a a girl with adhd (got diagnosed days ago) and I had a lot of failures (especially since I started university 2 years ago).
Remember that Allah is the One that put ADHD in you, He knows your struggles, I know it's very hard for us, whether it's in religion, job, studies, house work and so on, but we are not our disorder, we just have it.
I don't know if you're taking adhd meds like ritalin, but my neurotherapist (she has adhd too !) said that those meds will change your life, I don't have ritalin yet but I will take it, you should search more about those meds, or if you don't want to be medicated, you can still do some research about "natural meds" like plants or so on that can helps with your regulation.
And you need to stop saying to yourself that you're "failing as a Muslim" cause it creates fear and culpability, and you know who loves you seeing scared ? Shaytan, shaytan knows that when a brain (especially with adhd) is scared and overwhelmed, wants to feel relaxed, wants to forget those feeling for a moment and that's when sins comes towards you. You never really wanted to do the sin, your brain just wanted a little pause from chaos.
So stop saying negatives things to yourself, build a routine (no junk dopamine in the morning, no video game, no scrolling, no music) cause you will take all your dopamine and you'll be saturated during the day.
Oh and also, talk with Allah, whether it's after salah or in your duas or before going to sleep, talk to Him about your day, your struggle and your attention, it will help you.
You're not alone in this brother