Whenever I try to insert an unenchanted item into an Infuser, it simply won't accept the item. Because of this, the Infusers are unusable, even with max enchanting power.
Game version: 1.18.1
Mod version: 3.1.1

What item are you trying to place into the slot?
Are you using the menu or a hopper?
Have you found any items that do work?

What item are you trying to place into the slot? Are you using the menu or a hopper? Have you found any items that do work?

I tried with a Netherite Pickaxe then a Shield (both unenchanted), neither worked. I was using the menu (I did not place any hoppers near the Infuser). I haven't tried other items yet. Will test it out.

Just tested, those do definitely work.
When you put them in a vanilla enchanting table, do enchantments show up?

Also please try just this mod + Puzzles Lib in a new world and tell me if you still can't enchant anything.

I first tried using a vanilla enchanting table in a new world with all my mods intact, enchantments don't show up, even with lapis lazuli. Then I tried using just the infuser + Puzzle Lib mods in a separate installation, and the infuser worked just fine. By the way, if you're curious, these are the mods that my main installation has:
mods.zip

My guess then is another mod is storing some data for items as enchantments. I've seen that being done before, but it really shouldn't be, since this is exactly what happens.

Can you please try to find the mod that is responsible, so we can look further into it? You can do that by removing half the mods again and again until you've found the one responsible.

After painstakingly removing and readding mods one by one, I found that the mod responsible for the issue is Stackable Everything. Here's the CurseForge link of the mod: https://www.curseforge.com/minecraft/mc-mods/stackable-everything
A quick look at the mod's issue tracker reveals that the mod creator was aware of the issue, but couldn't fix it for a reason or another.

Yep, that seems to be it. Thanks for going through all of the trouble for finding that mod.
Closing this now as Enchanting Infuser is not at fault.