I have been very happy with the Fuji XF 500mm lens. I pair it with the X-H2s, which is "only" 26 megapixels, but it has a stacked sensor and is significantly and noticeably faster to focus than my X-T5 (which has the same 40mp sensor and focusing system as the X-H2 body.)
The X-H2s with the battery grip and the 500mm lens makes a fairly compact and lightweight package. I mean, for that sort of thing. The 500 is smaller than the 150-600 Fuji zoom, and a stop faster.