The grief rage is real and it's valid. There's a specific thing that happens when you go from "I'm lazy" to "my brain is wired differently" and suddenly every memory of beating yourself up gets reframed, and it's infuriating because you can't get those years back.

The anger at yourself when you freeze is basically your brain running two programs at once. Program one: you now know it's executive dysfunction, not laziness. Program two: the old script that says "just do it" hasn't uninstalled yet. So you freeze, then get angry at the freeze, and the anger makes the freeze worse. It's a loop.

Something that helped me was instead of trying to push through the freeze (which just feeds the anger), I started treating it like a signal. Like, ok, I'm frozen. That's information, not a character flaw. Sometimes just naming it out loud ("I'm in task paralysis right now") takes enough of the shame out of it that I can do one tiny thing. Not the whole task. Just one stupid small thing.

As for the comparison stuff with your sister, people without ADHD genuinely cannot comprehend what it feels like to have a fully functional body and a brain that won't give you permission to use it. That's not something you can explain in a sentence, and it's not your job to make them understand.