Vitamin E could be worth trying.
About eight years ago my younger horse got some scratches sort of thing on his leg. I chased it around (literally! Each patch of skin healed but not before infecting the skin around it) with antibacterial and antifungal treatments for months. This horse had always had the tendency to have any scratch or scrape below knees and hocks go fungus-y before it healed. Even a two drops of blood scrape would do it.
His vitamin E level was barely within the bottom end of the normal range when tested initially. Six months of supplemental vit E later it had dropped slightly, BUT the leg fungus had cleared up and new scrapes and cuts were healing without the fungus stage. I did increase his vitamin E and he tested smack in the middle of the normal range six months later.
He did get scratches in the fall of 2020 and they healed quite quickly with a little treatment. My older horse also got scratches at the same time and I was treating him much of the winter. I did add vitamin E to his diet when the scratches stopped responding to treatment.