Sounds like you know what you're doing. I semi relate to "the self-critical chatter in my brain that's obsessing over the past and the future. " I've done the self-critical stuff, but biggest problem would sometimes come with a racing brain when there were so many things going on in different directions that I was overwhelmed to the point where I felt like insanity would be just around the corner. One day maybe 20 years ago, I just shut it off. I'm not sure how. I just said, I'm not going to put up with this anymore, and it stopped almost immediately. I've never had one of those episodes again. If I had to guess, and this is only a wild guess kind of grasping at straws, it may have been something I would do to pointlessly punish myself in some subconscious way, for something that may not even be real.
Self criticism can be helpful, except when it's not. It might be better to think about what you do right than what you do wrong. Of course, there's always a happy medium between ignoring your inner self and focusing too much on it. But if you're not getting anywhere with the self-criticism, I'd let it go, if that's possible. I think it is, although I wouldn't have said that 20 years ago.