I was pleasantly surprised when I found my X-S10 could store and retain, ( even if turned off), my chosen aperture in any one of my 4 Custom settings if the lens aperture ring was set to A or the lens did not have an aperture ring. Is this now true of all the newer Fujifilm since the X-S10 was released?
At least on the X-T5 this is not possible, as already stated in another response.
When setting the aperture ring to A and adjusting aperture with a command dial the chosen aperture will be remembered when turning off and on the camera, but as a global setting, means also in the different custom settings (C1 to C7).
Below an overview of settings that can be set in the different custom settings.
Herbert