Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
The Sidebar is a launcher bar located on the right side of Microsoft Edge. If you enable this policy, the Sidebar is always visible. If you disable this policy, the Sidebar is never shown. If you don't configure this policy, the Sidebar's visibility follows the user's Microsoft Edge settings. As of Microsoft Edge version 141, the 'Microsoft365CopilotChatIconEnabled' (Control whether Microsoft 365 Copilot Chat shows in the Microsoft Edge for Business toolbar) policy is the only means of controlling the display of Copilot in the toolbar. Note: The recommended version of this policy-also known as the "Default Settings (users can override)" policy-is obsolete. This policy has never supported the recommended capability.