Computer Configuration > Administrative Templates > Microsoft Edge > Content settings
Both
HKLM\Software\Policies\Microsoft\Edge
OBSOLETE: This policy is obsolete and doesn't work after Microsoft Edge 87. This policy doesn't work because Flash is no longer supported by Microsoft Edge. Define a list of sites, based on URL patterns, that can run the Adobe Flash plug-in. If you don't configure this policy, the global default value from the 'DefaultPluginsSetting' (Default Adobe Flash setting) policy (if set) or the user's personal configuration is used for all sites. For detailed information on valid url patterns, see https://go.microsoft.com/fwlink/?linkid=2095322. However, starting in M85, patterns with '*' and '[*.]' wildcards in the host are no longer supported for this policy. Example value: https://www.contoso.com http://contoso.edu:8080