My baby doesn’t like ANY solids. Help! FTM

Ok so my 7 mo old which is really a 5 mo cus he’s preemie. The doc gave us the green light to start solids. We’ve been on cereal for about 1 1/2 months twice a day and he loves it. So we tried banana first. Hated it. Sweet potato hated it. Mango hated it. Apple nothing. So I bought different brands cus I was making it myself. Idk maybe he doesn’t like it that way? Maybe I should try mixing it with cereal or formula? Help! He’s under weight and idk wat else to do.