Platform level backups show a red exclamation point in the directory tree when trying to create a backup plan
This is caused by the Tivoli Storage Manager for SharePoint Agent not being installed on the SQL server. Platform level backups backup the content DBs where Granular level backups do not. As such an agent is required to be installed on the SQL server in order to do this.
Resolving the problem
Install the same level of agent on the SQL server as you have installed for the rest of the farm.