bucket policy vs IAM roles policy

I have a bucket policy mentioning some roles with only get and put object permission. I also have another Role and a separate policy attached to it having multipart upload permission along with KMS decrypt and generate data key permission attached to lambda function. While lambda execution , getting assumed role/lambdaname does not have generatedatakey permission. But the permission is there for the role. Should i add this role along with all permissions in the bucket policy. Does it have preference? I do have S3 vpc endpoint and kms:generatedatakey and KMS:Decrypt is not present there. Should i mention it there.