Windsor Castle played a major role in all seasons of The Crown.
For seasons 1, 2 and 3, Belvoir Castle in Leicestershire was used to represent Windsor Castle.
The history of Belvoir Castle dates back to the eleventh century. It is the ancestral home of the Duke of Rutland, where the family has lived in an unbroken line for nearly a thousand years. The castle and gardens can be visited (https://www.belvoircastle.com/).
From Season 4 onwards, the scenes were filmed at Burghley House in Lincolnshire.