The initial creation of an attachment attribute creates as read-only
STEPS TO REPRODUCE:
In MUX-
Expected Results: The attachment attribute will have an icon where you can add attachments
Actual Results: The attachment attribute seems to be read-only
Release : 16.1.0
DE70544
Fixed in 16.1.1
Workaround:
Open the new attachment attribute you created and then click 'Save and Return'