From the Disney site:
Check Back Soon to Purchase. Beginning May 31, 2023, the Disney Dining Plan can be added to Walt Disney Travel Company packages that include a Disney Resort hotel stay with arrivals on or after January 9, 2024.
Dining plans are not available for vacation packages with arrivals through January 8, 2024 or for individual purchase.
Check Back Soon to Purchase. Beginning May 31, 2023, the Disney Dining Plan can be added to Walt Disney Travel Company packages that include a Disney Resort hotel stay with arrivals on or after January 9, 2024.
Dining plans are not available for vacation packages with arrivals through January 8, 2024 or for individual purchase.