Some are reporting 'spacing options' on Reddit (they do not cite which version other than 'the latest'):
https://www.reddit.com/r/kindle/comm...ing_is_my_jam/
In the interest of scientific inquiry, I updated my Paperwhite to 5.18.4. It took 4 attempts to update my Kindle Paperwhite (11th generation) for some reason; it kept saying 'invalid update file', but I'm quite certain it was the correct one and that I had waited for the copy to complete before ejecting. And - drumroll - the spacing options are not there.
de-DRM of KFX works, at least for now.