By implication it is.
Your statement, once allowed to join Congressional approval is needed for any change in their status is not true. Only the specified situations trigger empowerment.
Joining to begin with, changing borders, splitting up, combining with another state are all listed. Again, it permission is needed to join or change, why shouldn't it be needed to leave?
Amendment X tells Congress that if a power is not delegated to it by the Constitution, it aint a Congressional power.
And the Constitution clearly states that the power to admit a state and approve changes in status once it's been allowed to join is a power delegated to Congress.
You are amending the Constitution, partner. That document is worded exactly as it is for good reason, but you are trying to make it say what it doesn’t say.
If it means you you claim, then Texas would have never been allowed into the Union, because its founding document specifically allowed for succession.