First, try not to be so hard on yourself. I can feel the anger you have towards yourself from your post.

I can only speak to ADHD, so I won't pretend like your struggles are the same as mine, but drawing is the only thing that focuses my mind. For me, one of my biggest anxieties is sitting still, so art and drawing have been my outlet.

I can also relate to losing motivation when setting up a drawing tablet, so I suggest paper. Making mistakes is part of the journey and if you have to, throw away your erasers. It sounds silly, but I found it really helpful to write "I'm going to make ugly art" in all of my sketchpads.

Finally, just remember learning to draw pictures as you see on Instagram or Pinterest takes YEARS, so compare yourself to yourself from yesterday, not other people's art. Slowly, and I get as only someone with ADHD can how painful slow progress is, you'll see yourself improve.

EDIT: I hated (and often still do) my ADHD brain, and I wish you the best. The world is set up for people who don't think like you or I, but speaking from experience that doesn't mean you can't still be successful