Hi Rebecca,
Thank you for posting this.
Before we proceed can you confirm the brand/model of the mouse that you are using, also is your mouse tri-mode or only wired? since Windows 11 handles hardware drivers and scrolling differently depending on the device, especially for Microsoft.
For the issue itself, after upgrading to Windows 11 this commonly happens due to reset mouse settings or File Explorer not refreshing input states. First, go to Settings > Bluetooth & devices > Mouse and make sure the wheel is set to scroll multiple lines at a time and that “Scroll inactive windows when hovering over them” is turned on, as this directly affects File Explorer scrolling behavior. If scrolling works in other apps but not in File Explorer, restarting Windows Explorer from Task Manager often fixes it immediately and is a Microsoft supported step. Uninstalling the mouse under Device Manager > Mice and other pointing devices and restarting the PC forces Windows 11 to reinstall a clean hardware driver.
You can use this link for further guidance and reference: Change mouse settings
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Best regards,
Yaj S.