Hello @Prasanna S ,
I'm not sure what are the exact GPO settings that are applied but adjusting the GPO could fix your issue (removing black screen) and you should then be able to see UAC.
Set to disabled:
Security Settings > Local Policies > Security Options > User Account Control: Switch to the secure desktop when prompting for elevation
Hope it helps and don't forget to upvote.
Kind regards,
Domagoj