Same for me. I bought a Lamy Safari fountain pen with a triangular grip that sort of forces me to hold it the “right” way, and it was transformative. What, handwriting can be pain-free? And I don’t have to consciously remember to adjust my grip because it pushes me that way? Miracles!
More info here: https://www.themanual.com/culture/different-types-of-pencil-...
My hand wants to use the lateral tripod grip by default, leading to me gripping the pen too hard and my hand hurting. The Safari gets me to use the dynamic tripod grip which is vastly more comfortable. They’re both considered “mature” grips, but one is much better for writing lots of text in one sitting.