What do you mean “does not allow you?”
With the newish freedom to apply, you do not need your boss to approve you being considered for an internal job posting. You can apply directly and the new team decides whether to interview you or not. The HR email states 1+ yr is the new baseline to be considered for internal mobility
Then if you are selected, your boss would need some pretty significant justification to block you.
If you do not apply, your boss takes the easy route as they don’t have to explain to HR/upper management why they blocked someone from moving