In most cases, you do not need to disclose an external interview process before you have a reason to act on it.

Your relationship with your manager matters, but so does the practical risk of announcing a possible departure that may never happen. Use vacation, personal time or normal scheduling flexibility where you can.

Earlier disclosure can make sense if the process materially affects work commitments, your manager is actively supporting your transition or your employment agreement creates a specific obligation.

Otherwise, wait until you have a concrete decision to make. When you do tell them, focus on the career move rather than making the conversation about dissatisfaction with the current team.