Is it possible to have different button to be the default available on the same screen for different roles?

Yes it can be done but see below for some limitations depending on your full intent.

I don’t believe this is possible with the basic/low code Visual Workflow Customization as User Role is not a workflow identifying field so you couldn’t have full separate flows by Role

This could be addressed by creating a custom Workflow at the coding level.

this could be done by setting up different State Conditions by Role

Open for CSR and Open for Whse for example at the coding level. The screen presentation would then differ based on those states depending on the user security viewing them.

This could also be achieved by Event handling on the screen.

If you want both buttons to show they can both be added in Workflow

The hiding/showing of buttons can be addressed another way by role thru the security settings. As long as you would never want your Cust Svc rep to Confirm Shipment and your Whse to never Print Confirmations

You can add both buttons to the Workflow State toolbar 

Then remove the access of the Confirm Shipment btn from the Customer Svc Role &

Then remove the access of the print Confirmation btn from the Warehouse Role