This is a recurring issue over the years with Ripley , and with all foods.
I've always offered multiple pellets at a time for him. It'll take him weeks or months to try out a different pellet, then he'll eat it for a while, then he's done. Zupreem has been the only pellet he'll always eat. I've been rotating through Zupreem, Lafeber, Hagen, and Harrison's for the past several months , and the only one he was eating was Zupreem. Now it's none.
And he won't eat the natural Zupreem, but only fruity usually. And his preferred color changes. Before he stopped eating them completely, he was only eating yellow and green.
Ones he's eaten for a while then decided he didn't like anymore: Hagen Tropican, Psittacus Omega, Harrison's Pepper, Pretty Bird African Grey
Ones I've offered multiple times and he refuses to try: Roudybush Maintenance, Zupreem Natural, Kaytee Exact, Kaytee Nutrisoft, Harrison's Adult Lifetime, Higgins in tune, Psittacus Maintenance, Psittacus High Energy, Lafeber Pellet Berries, Lafeber Daily Maintenance, Lafeber Tropical....
I'm sure I'm missing more. The point being it's not a new issue, Ripley is an old stubborn man, and I'm sure he finds a weird joy in worrying me. I would just abandon pellets completely, except sometime in the future, he'll decide he hates veggies again, and then I'll be scrambling trying to figure out what he will eat. Because he doesn't stop eating something because he prefers something else in the bowl. He just decides he's done, regardless if a backup is available.