Is it bad to let baby sleep in carrier or rocker in the day

First time mum here. Feeling very anxious now because I saw on a reel on IG about ‘container baby syndrome’ saying that it is harmful to let baby be in a carrier or rocker for long hours and it will delay their physical development, cause flat head etc. My baby is 3.5 months old and since 1 month old, I have been letting him nap on the rocker in the day, or in the carrier if he needs to be held. Did I make a mistake and cause harm to my baby? 😭 In fact, he does have a little flat head and hasn’t shown any signs of wanting to roll. I’m worried it’s because I let him sleep in rocker and carrier… Any babies who sleep in rocker or carrier for long hours and turned out fine? I feel so bad as a mum and I need assurance 😭