That was a show-stopper for me. I have so many 4k UHD files that play beautifully on plex but not so hot on jellyfin. I support jellyfin though, there needs to be competition in this space so plex doesn't run away with the 'ball'.
I've had no issues transcoding with tone mapping in Jellyfin, on both an Intel iGPU and a GTX 1660.