Adding fertilizer will often not work. Adding chelated iron, like EDTA-Fe2+ or EDDHA-Fe2+ does. The chelating agent makes it soluble and prevent it from forming insoluble salts with other minerals. So it makes it bioavailable in a way larger pH range. Which pH, depends on the chelating agent. If you add a tiny pinch of this to a glass of water. This will make it very red. Then dilute it until you can barely see it is pinkish. And you can add that to your plant.
The issue is not that iron isn't there. The issue is that because of the pH or the roots not working like they should, it likely isn't isn't available or being taken up by the roots.
Vabomix1 is an organic fertilizer. Organic matter contains trace elements. Just not immediately bioavailable ones.
Osmocote should have chelated iron in there as well. As it is a chemical fertilizer but with trade elements. But not 100% sure because some consumer versions seem different or have an incomplete label.
If you dilute the iron only in water, then you can even leverage leaf uptake. Not sure how supergood that works. Never did a proper experiment. But theoretically it should work. But if the leaf uptake of iron works, it can help plants with weak root systems that have iron chlorosis. A wetting agent would help even more, but I never used that.
