That is what the WDW website says:
If you have a room-only reservation at a Disney Resort or other select hotel for a stay in 2021, please
call the Disney Reservation Center or call your travel professional beginning on June 24 to upgrade to a vacation package with tickets—
and then make your theme park reservations.
Want to Book a New Vacation?
By June 28, all Guests will be able to purchase new Disney Resort hotel packages and theme park tickets
and make their park reservations for arrivals starting in 2021 as our phased reopening continues. Guests will be able to view park reservation availability online prior to purchasing their tickets.