I’ve been through all of this myself, and I empathize.
Since you’ve tried all the apps, and they don’t consistently work for you, … that means it’s not the apps 
I do understand you’re looking for something that will help.
One of the most helpful things I’ve found is the book linked below. It’s full of practical and actionable advice, not the BS you’ve probably read elsewhere like “be intentional.” (Yeah, thanks for that.I had no idea.)
When you’ve studied the book for a while, start to think about your own System. How do you do things? What happens in this situation, or that situation? Write it down and make yourself instructions. If something works, make a note that it is working. If something can be improved, rather than jettisoning the whole system, think about how it can be improved. If your task manager app becomes overwhelming after six months of use, try to find a strategy to prevent that from happening. (Such as weekly and monthly reviews.) I even have templates for meetings with prompts like, “What do I need to do to avoid being blindsided?”
As I’ve said, I’ve been through this myself, and am practicing this method. (I like that lawyers, doctors, etc. say they “practice law”, or they “practice medicine.” I guess I practice being a grad student, and practice being John. I call this The System (to myself, and in my notes). Anyway, so the beginning of last week, I noticed I wasn’t getting much done. I thought about this for a while, trying to think about why I was struggling. One of my previous gotos might have been to try a new task manager, but since I’m now working on The System, I just thought things through. I finally arrived on my office being a mess (picture posted elsewhere). I cleaned up, and things are returning to normal.
There are a few apps and services I use that I find helpful:
- NotePlan - this is where I take notes, schedule things for the day, list next actions for projects, and do my reviews (some projects as often as daily, but usually weekly). There are a couple of things I would like for it to do that it doesn’t, but I’m sticking with it because the grass is not greener elsewhere, it’s just different grass. Maybe even with cow pies in it.
- Freedom - block MPU, and Twitter, and email, and Teams and Slack and all those other places you go for a little hit of dopamine. I’ve learned that even if I’m waiting for data to process, switching over to, say, Twitter for a quick update is detrimental to my overall focus. So now I just sit and wait, take a bio break, etc.
- Timing - tracks where my time goes. It is very granular too. You can easily create rules so that time spent on, say, my school’s website goes to Teaching, and time spent on MPU goes to Social. You can also assign degrees of productivity to projects, so some things are figured as more productive than others. Daily, weekly, etc. reports show where your times goes, and gives a productivity percentage. These numbers let you gamify it, which ADHD brains seem to like.
- How to ADHD - short, informative videos
Finally, this is about learning to understand yourself and work with yourself. So above all, be good to yourself. Try not to beat yourself up about things - you’re learning.
As may be apparent, I’m an open book, and open to questions here, or by direct message (from anyone).
https://www.amazon.com/ADHD-Pro-Sustainable-Productivity-People/dp/B096LS2PYS