> Does fido-mode use the flex completion style unconditionally, ignoring the user's setting of completion-styles and completion-category-overrides?

Yes.  That is by design.

If you want to tweak, you should be able to use

minibuffer-setup-hook for that. I think Dmitry wants

to add some new variables to allow fido-mode

specific settings, but don't think that's a good idea.

That's not to say this shouldn't be easier, but I think adding

variables to fido-mode is not the way to go. Could end

up with fido-specific versions of every such variable. I prefer

to review the other variables, their values and semantics

so we come up with a holistic solution.  For Emacs 28.

João