The bigger the fish, the more stubborn they typically are.
I have trained over 100 fish to eat pellets that were typically hard eaters. Some harder than others.
my experience is that all these methods above can be used. But one thing that has really been an extremely big factor in the training process that I haven’t seen anyone mention here yet. Teacher fish. Get some silver dollars (my favourite) or tinfoil barbs. They eat anything with gusto.
always feed in the same spot so they get used to food being there. Start with smaller amounts of dusting as was previously mentioned. Then slowly decrease the food they are eating, and increase the dust into bigger chunks and eventually full pellets. Always soak the pellets so they are easily chewed. Once they get used to the pellets you don’t need to soak them as much.
in training roughly 40-50 different bass to take pellets in this way I have only lost 1 to starving itself. It never ate from the beginning and started out very skinny. It lasted 2 months at 2-3” and never ate as much as a single bloodworm as far as I saw. I suspect it had worms before I landed it as a wc ocelaris.
also I typically dump the new food in really fast in short bursts to trigger the feeding response. Pump returns are great for this as well depending on the set up.