It says EBS can only be attached to one volume at a time but the aws documentation says theres ebs multi attach?
You can attach an EBS volume to multiple EC2 instances (called Multi-Attach), but that is a very specific use case with need-to-know constraints, such as:
Limited to Provision IOPS SSD type only (
Limited to those supported regions of Block Express volumes for both
More limitations as described in Attach a volume to multiple instances with Amazon EBS Multi-Attach
So generally speaking, an EBS volume is single-attach, with exception of multi-attach under very specific conditions.