From current AWS documentation:

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/volume_limits.html

T3, C5, C5d, M5, M5d, R5, R5d, and z1d instances support a maximum of
28 attachments, and every instance has at least one network interface
attachment. If you have no additional network interface attachments on
these instances, you could attach 27 EBS volumes.