The Portfolio "Team" field is currently locked. This makes it impossible to make this field required in field configurations.
An important use case is when you have multiple teams using the same project. To be able to separate the different Team's board filters you would want to use the Team field. To make this work you need to make sure field is always filled in to avoid new issues from disappearing from the boards.
When creating an issue and committing this to Jira, you must make a field required in the field configurations. To use a scripted validator will not work in this case, as this will cause an error.
Unlock field to make it possible to use in field configurations.