Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
Define a list of sites, based on URL patterns, that cannot be opened in sidebar. If you don't configure this policy, a user can open any app in sidebar. If the 'HubsSidebarEnabled' (Show Hubs Sidebar) policy is disabled, this list isn't used and no sidebar can be opened. For detailed information about valid url patterns, see https://go.microsoft.com/fwlink/?linkid=2281313. Note: A blocklist value of '*' means all apps are blocked unless they are explicitly listed in the 'EdgeSidebarAppUrlHostAllowList' (Allow specific apps to be opened in Microsoft Edge sidebar) policy. Example value: https://www.contoso.com [*.]contoso.edu