I don’t feel especially well poised to give advice here, because I’m still struggling with this, but maybe that’s the point; increasingly, I think that my idea of what “coping well” means is false and unattainable, and that real progress involves a bit of self acceptance.
On that front, my advice would be that living with ADHD means learning what battles are worth fighting, and only you can figure out.
A friend of mine used to struggle with extended chunks of work of one kind, and she spent a long while trying to force herself to work with timers and stuff, but her actual productivity shot up when she gave herself a bunch of tasks to cycle between. She enjoyed breaking up work with household tasks like washing the pots, because it’s simple, and has a defined end. Amusingly, sometimes she’d work at my place when we were students, and she’d tidy up for me and later say thank you for the opportunity.
One of my issues was I kept expecting myself to remember stuff when my short term memory is trash, even by ADHD standards. I got better at training myself to write stuff down, including sometimes asking for a break in the conversation to give me a chance to write it down so I don’t forget. That was awkward at first, but it got easier, and most people were understanding - most people seemed to respond positively in fact, because it shows that you care about what’s being discussed (certainly more positive than if I’d forgotten and incorrectly given them the impression that I didn’t care)
I spent a long time trying out different apps and systems, because novelty seeking brain wanted a silver bullet to solve all the things. Sometimes I still fall into that trap, but nowadays I know that even the best todolist or calendar app in the world won’t help if I don’t use it. It’s a me problem, and integration problem. Part of what helped me there was actually evaluating where my various systems kept going wrong. Like instead of calling myself lazy for not keeping things tidier, I made actual progress by buying a bunch of bins so that there’s always one at hand. I stopped berating myself so much. Beating yourself up for not being able to do things is internalised ableism.
Medication helps a lot, but I found that there were a bunch of maladaptive coping measures I’d built up over the years that I had to unlearn once I had medication. And then when I had a period without medication, I found myself struggling more than ever. It’s a combo approach, is what I’m saying. Don’t expect yourself to function at the same level as you would if you were medicated.
What you describe reminds me a lot of 
about how untreated ADHD traps you on depression.
In the past, with similar issues, I’ve had good success with requesting the book on Zlib, especially newer books.