Let me say that I do not have a Fuji camera but I have Olympus cameras with focus bracketing. I previously posted a document on using focus bracketing for macro-photography using the Olympus 60mm lens.
( https://www.uglyhedgehog.com/t-623714-1.html ). Some of the small details may differ for your camera but I am sure the process is similar. Olympus also posted a discussion on focus bracketing for landscapes.

https://learnandsupport.getolympus.com/learn-center/photography-tips/landscapes-nature/using-focus-bracketing-and-stacking-in-landscape?utm_content=petertipcta&utm_campaign=2020_03_Focus_Stacking_US&utm_kxconfid=t5ljhtrz5&utm_source=email_ettips&utm_medium=email&sfmc_sub=203456726

The process appears to be similar on your Fuji camera. The working parameters are the step size and the number of steps. It is true that these steps are not well defined but I suspect these are focus motor steps and do not strictly relate to a specific distance interval. You will need to do a few experiments to use this feature effectively. The focus motors appear to be a type of stepper motors.

On the Olympus camera the step sizes are 1 through 10 and the number of steps is 2 to 999. I cannot imagine using 999. If you set too many steps the sequence will stop when infinity focus is reached.

If the step size is too large your focus stacked image will be unsatisfactory as portions of the image will not be in focus in any of the images. If it is small you will need to use more steps but otherwise no harm is done.

Small step sizes are very good for macro and larger ones for landscape.

If you are shooting landscapes if you choose too few steps you will not get to infinity focus.

You might find it handy to take a shot with your finger in the frame before and after the sequence for focus bracketed shots.

I hope you will find thus useful.

From what I understand that you are trying to do, it will help immensely if you have a tripod or at least a monopod, and also very still conditions. As in an early morning before the breezes have stirred up.
You can do quick stacks, with a small number of frames, by simply turning the focus ring a little. Do several 'runs', and attempt the stack with picture frames that line up the best. There will be artifacts with this method because of movements, but these can be patched up later. A stacking program like Zerene Stacker has tools for selecting which bits of the original picture goes into the stacked picture. But those tools can't do everything although it can do basic fixes are very quickly and it requires no particular skill. Then there are more powerful programs like Photoshop or Gimp (Gimp being free), which provide cloning and healing brushes that can do fancier corrections. Here is an example, taken from a few pictures by simply turning the focus ring. There were artifacts that remained, where parts of the wings did not line up. But those were corrected in Gimp by cutting and pasting them into alignment, and then using cloning and healing brushes to conceal my work.
Best to view in download.