I can select an item/fluid to craft easily enough, but for some reason the Craft & Usage buttons do nothing when clicked. They are clickable. They just don't do anything. The Info button also doesn't do anything.

Closing & Opening the window again show the selected items in the "Previous Item" list, but I still can't do anything.

They just don't do anything. The Info button also doesn't do anything.

Well, they don't work if nothing is selected in the selector on the left-hand side.
The history buttons are independent of this, they work with left/right click

yes the translation and the info are not ready yet. because this is the lowest priority.

I mean, even when something was selected the craft button didn't do anything.

It has to work, otherwise nobody wouldn't be able to work with it at all
we have to find the difference (in the usage)
which item did you select? only item or fluid works. if that is the problem

I tried fluids, science packs, modded science packs, nuclear reactors, heat pipes, batteries, inserters, steam, molten iron, fluoroketone, e.t.c.

The console message that appears when starting the game says "Factorium: 801 items, 73 fluids, 4190 recipes, 0 research items"

unfortunately i can't reproduce this. and i don't have enough information about your game status.please
use the upcomming version. if the error still persists, please contact me again.

Here is the link to the save file if you want to look deeper : https://mega.nz/file/VtQlRYLT#LE2kaOSJHVixaeal4RiF0AnaqhCgEYlZOkI_sEnycts

Unfortunately this issue seems to be surprisingly common, and not being able to reproduce it is... odd to say the least. Let me elaboreate:

Having thought it might be mod interaction, I have cleaned up factorio to current stable version, and removed all mods (including this one). After first restart, I then redownloaded Factorium [3.0.3] and Your library [version 3.15.15, as listed as requirement]. Then I started both a new game, and previous save, both on current stable version [2.0.42], and on current experimental build [2.0.43]. All tests were performed on Steam version.

In all cases neither of the following worked, in either of those testing conditions (with a minor caveat, that I will list):
- Craft button does nothing
- Usage button does nothing
- Information button does nothing

Caveat: When window is closed and reopened, both buttons add an item/fluid icon [one that was selected to the left of the button when button was pressed] to the list below the buttons. Once for every reclick.

When running with debug mode on, Factorium shows correct load of recipes, but no further debug information is provided when clicking on buttons.

When running in my full mod layout the only thing that changes is that Factorium seems to be incompatible with Transport Drones mod.

since i'm already working on the next version, i can't say anything more about this release, except: wait and use the upcomming version.
The mod is marked as WIP (Work In Progress) so see each version as a (mostly working) preview.