Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
OBSOLETE: This policy is obsolete and doesn't work after Microsoft Edge 136. This policy provides a temporary opt-in back to a deprecated and removed set of platform events named Mutation Events. If you enable this policy, mutation events will continue to be fired, even if they've been disabled by default for normal web users. If you disable or don't configure this policy, these events will not be fired. Note: This policy is a temporary workaround and will be obsolete starting with Microsoft Edge version 137.