Meikon is already offering several waterproof cases for Fujifilm X series cameras.
Now they have also launched the Meikon SF-X-T4 waterproof case for Fujifilm X-T4 cameras and it so so far listed at their website here.
As for the Fujifilm X-T4 in particular, there is also the Ikelite 200DL Underwater Housing for Fujifilm X-T4 (as well as other Fujifilm cameras).