Live and frozen foods are the best. I would very highly recommend frozen bloodworms, mysis shrimp and krill.
You could also try offering it a gel food mix. I make my own with blanched vegetables (blended to a pulp), frozen bloodworms and mysis shrimp, some ground high protein pellets, and mix it all together with hot water and gelatin. It’s a great staple because it’s very high protein, and also gets them their veggies. If you don’t want to make your own gel food, then you can also buy pre-made gel food that comes in powder form and and you just add water and mix.
Most tropical flakes are total junk. Most of them are made primarily from soy and meat “meals”, which aren’t really meat. Meat “meal” is heavily processed and often includes ground bones, hooves, eyes, etc. whatever parts of the animal they cants sell elsewhere.
If you are going to feed it any kind of dry food, then use Omega One, preferably some kind of sinking pellet. Omega one is meal free, and is one of the most quality fish food brands out there. They also have a couple great pellet mixes deigned for catfish.
I’ve put links to a couple good bottom dweller pellet mixes.