I know how frustrating this can be. My DH used to do that too. When I finally realized he is as certain of his version of events as I am, I was able to resist the urge to convince him of the truth. I realized he was unable to participate in the robust conversations we used to have and I looked to friends and family for that. With DH I simply agreed with his take on things rather than risk making him feel like I was gaslighting him. It took me some time but eventually I would simply say something noncommittal like "Wow" or "interesting ", because, ultimately, it didn't really matter and his brain could no longer reason. My mental health improved once I accepted this new reality. I know it's hard at first but becomes natural pretty quickly.

I hope this helps. You're not alone. I'm glad you are here and reaching out for help. There's lots of support on this forum.