I’ve written about it elsewhere in greater depth, but here are the headlines:
Although it is based on SSIS Scale Out, you can’t actually configure SSIS Scale Out to run on the instance. If this confuses you then read my in-depth post.
SSISDB is installed in either SQL Azure or on a Managed Instance.
You don’t have to create Integration Services Catalog/SSISDB yourself; it is done for you. So that annoying key management is no longer a problem.
Richie’s got more to say on the topic, so check out the highlights and then his in-depth post.