The physical editions, which were previously planned to ship on the same date, have been pushed back by two weeks due to a small number of issues that needed to be fixed in the console ports, slightly delaying manufacturing.
OMORI first launched for PC via Steam on December 25, 2020.
Here is an overview of the game, via OMOCAT:
Explore a strange world full of colorful friends and foes. Navigate through the vibrant and the mundane in order to uncover a forgotten past. When the time comes, the path you’ve chosen will determine your fate… and perhaps the fate of others as well.