My toddler does not like our newborn 😭

My toddler does not seem to like our newborn. He randomly runs towards where our newborn is laying down and slaps him! Gosh 😭 I have done everything but nothing seems to be working.. my toddler has always been included in activities with my newborn, I always make sure that I spend one to one time with my toddler... he isn’t left out at all so why is he acting this way? What can I do to stop this behaviour? A few hours ago, I put baby on his bouncer swing while I warmed up his milk, I heard scream from where I had left him... I ran there and saw him on the floor!!! My toddler managed to remove his seatbelt and pushed him to the floor... I didn’t even know he could remove seatbelts!!!! I cried so soooo much and I felt so numb... I didn’t know what to do! Guess what? My toddler was laughing at what he did