Copilot must be disabled.

The Sidebar is a launcher bar on the right side of Microsoft Edge's screen.

If this policy is enabled or not configured, the Sidebar will be shown. If this policy is disabled, the Sidebar will never be shown.

Disabling Sidebar will disable Copilot.

Verify the policy value for "Computer Configuration/Administrative Templates/Microsoft Edge/Show Hubs Sidebar" is set to "Disabled".

Use the Windows Registry Editor to navigate to the following key: HKLM\SOFTWARE\Policies\Microsoft\Edge

If the value for "HubsSidebarEnabled" is not set to "REG_DWORD = 0", this is a finding.

Set the policy value for "Computer Configuration/Administrative Templates/Microsoft Edge/Show Hubs Sidebar" to "Disabled".