Hello,

As a team administrator user I want to have an option to prevent any repository creators from making a repository public

This would be accessible when creating a group or editing a group

Settings > Access Management > User Groups > Create/Edit

If this option is enabled the user in the group is presented with the "This is a private repository" option next to "Access level" on the create repository screen. If it is disabled the option is hidden or grayed out with the value set to private"

An example is provided below

Setting:

If enabled:

If disabled: