Not able to create SSISDB catalog
I had this problem and it wasn't related to user permissions.
I had done an earlier install of SQL server and chose to install many options except for 'Integration Services',
so I ran the SQL Server Installation Centre application again and this time chose to install the 'Integration Services' feature.
I think that the reason I could see the 'Integration Services Catalogs' node in SMSS despite not having installed 'Integration Services', was due to choosing to install 'Master Data Services' during my earlier SQL Server install.