Cross account connection between two AWS accounts on same zone

You don’t technically create a cross account connection.

You have to grant access to the S3 bucket and to the KMS key in the target account using policies.

Please find the 2 pages you will require to grant access

https://docs.aws.amazon.com/AmazonS3/latest/userguide/example-walkthroughs-managing-access-example2.html

https://docs.aws.amazon.com/kms/latest/developerguide/key-policy-modifying-external-accounts.html#

Of course the user/role in source account will need permissions to access s3 resources and Kms functions set in source account also.