A lot of people have been asking about that lately.
The reason why the gallery hasn’t been available yet is because everyone who has worked on the project (including Eight/Poppu) have been busy working on other projects or worrying about their affairs outside of both development for this series and/or whatever else they are working on on their socials at the time.
I get that a lot of people are itching for seeing all the artwork and hearing what the characters were saying within the game much like the gallery options for the first game, but updating certain aspects of a game to add some extra stuff takes quite a bit of time.