Hi Jennifer,
Good day, and thank you for reaching out to the Microsoft Community.
After reviewing your scenario and performing some research, this behavior appears to be related to the current functionality of Outlook rather than a setting within your organization. Because of this, there does not appear to be a setting that administrators or end users can enable to allow searches across Calendar Groups.
I completely understand how important this can be, and it’s a situation many others may run into as well. As sharing this kind of experience can be helpful for the product team when considering future improvements, I strongly recommend submitting your feedback through the Outlook Feedback page. Customer feedback plays an important role in influencing product enhancements, and your voice could help bring attention to a feature that many people would truly benefit from.

Just a quick note as well: this is a user‑to‑user support forum. Independent advisors, including myself, are regular users too and don’t have the ability to change or influence Microsoft product features or design decisions. What we can do is share findings, observed behaviors, and practical tips based on experience and available information.
Once you've submitted your feedback, feel free to share the link here in the comments. I’ll be happy to upvote it to help bring more visibility.
Additionally, since many other users have raised similar concerns but may not be aware of where to submit product feedback, if my response has helped clarify the situation and pointed you toward a possible next step, please consider upvoting it. Doing so can help make this discussion more visible to others in the community who may be experiencing the same issue and are looking for guidance or a way to support similar feedback.
I hope the information helps guide you to the next steps. Please feel free to reach out if you need further assistance.
Thank you again for your time and for raising this important usability concern.
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