Difference Between io2 Block express and Io2 ?

io2 = very high performance
io2 Block Express = extreme performance (but with instance + size limitations).

What is Nitro instance ?

It is a modern EC2 instance types that use the AWS Nitro System.

How Delete on termination is handled for multi attach ?

Delete on Termination only applies to the EC2 instance that created the volume attachment. If multiple EC2 instances are attached to the same volume (via Multi-Attach), deleting one instance does not delete the volume unless delete on termination is true.

Does Provisioned IOPS has restrictions in region ?

Yes, Provisioned IOPS EBS volumes have some region-specific restrictions and limits.

Can we modify volume for Multi- Attach ?

Yes, we can modify an EBS volume that is enabled for Multi-Attach, but with certain considerations