I suspect it may be a wontfix, but it's such a popular mod - I really hope you'll consider it.

At the moment, in "Factory planner"'s interface, all recipes and items are shown. (e.g. https://i.imgur.com/dTzKKua.png) Integration such that the appropriate items/recipes are hidden inside Factory Planner would have been fantastic.

(Factory Planner already has a built-in "Show unresearched recipes" / "Show hidden recipes" toggle for certain parts of its interface; but that unfortunately doesn't relate to the picker in my screenshot above, nor a couple of other places.)

Depending on how Factory Planner populates that UI, this might already be handled.

In the mod settings for "Hide Space Age spoilers", uncheck the "Only hide in Factoriopedia" option. This straight up tags things with the "hidden" flag instead of just "hidden_in_factoriopedia".

I imagine that Factory Planner would not add "hidden" items to that UI.