Great job! This was a really inspired game with nice art, sound, and game feel. I could tell after 3 playthroughs your level design was pretty thoughtful, and intentful, and does a decent job of self teaching the game mechanics. I liked it a lot. The animation of the assigned weapon is nice and the art/ui is simple and cohesive. I have some feedback
For accessibility, it might be nice to make the arrows work for left-handed players too. I also would consider playtesting your game with a color blind simulator to see if it still looks good under that condition. Add a pause screen, especially for those quick alt-tab moments, and a volume slider. The enemies kinda remind me of pig noses, in fact it was impossible to get out of my head.
Maybe consider adding a custom cursor for additional polish. You could probably add a bit more impactfulness when the play is hit by the final blow, such as a flash or bounce and scale effect, or a . Adding some color to the main menu could highlight the elemental resistance thing nicely.
And on the "wrong element," maybe think about switching it to "same element?"
I noticed you can pickup items you already have and can switch to an empty weapon slot.
This was an amazing game, great job.