Not keeping up much with the seeming increasing rate at which new bodies are released by manufacturers, I must admit I'd never even heard of the X-H1.
Looking at the comparison on dpreview
here, it seems that the X-T4 is better in almost every respect - is the body size/shape nicer in the hand, which is why some who've used both prefer it? I like the look of the screen on the top, I must say.
If you can't be bothered to click, the conclusion:
"There's a sense in some quarters that the X-H1 was prematurely abandoned by Fujifilm when, as the last model of its generation, it didn't get all the features introduced with the X-T3. But comparing its v2.00 IS behavior and performance to its original state, you could almost argue it got a taste of X-T4 tech, over a year early.
Overall, the X-T4 pushes things forwards in almost every respect, even if it's not necessarily meant as a like-for-like replacement. And it does so with a list price $200 lower than the X-H1 at launch.
If you can find an X-H1, it's still a fine camera, especially if it's at an appropriately good price. But the X-T4 is more capable in almost every respect and to a degree that will be an appreciable improvement across a wide range of photographic and videographic situations."