Did open the door to, granted (8)
I believe the answer is:
admitted
This clue could be a double definition.
'did open the door to' is the first definition.
The answer and definition can be both to do with fundamental existence as well as being past participle verbs.
Perhaps there's a link between them I don't understand?
'granted' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for admitted that I've seen before include "Owned up or let in" , "Allowed in or accepted as true" , "taken into hospital" , "income?" , "Conceded; let in" .)