Help!! Betta won’t eat

This is Kurt my male blue orchid crown tail betta I never got into aquariums before this but I saw him at the store and just fell in love with how gorgeous he is. I went down the rabbit hole of what he needed and how to care for him. I’ve had him for about 4-5 days now and he hasn’t eaten at all. And the past day or so he’s just been swimming at the top won’t even go down to hide or go anywhere else at all, when he was acting just fine before (curious and exploring the tank). He also has been constantly flaring up at the side every couple of minutes, and I just frankly have no idea what else to do

5 gallon tank 6.5 ph 80 degree water 0 ammonia 0 nitrite 0 nitrate 2 live plants (Anubis and Amazon sword)