Hi there! So, from what I myself understand, as the game progresses and Meyaoi completes a new romantic route, those of us with beta access should receive an email telling us about the update and we can download the latest version from this itch.io page.
As for when we should expect the first Beta version, it was original meant to come out sometime this January-March, but while Meyaoi will still try to make that deadline, it's very likely been pushed back a bit so she can release a Beta Route with all the side-quests, festivals, and mechanics completed.
Meyaoi is pretty good about updating her Twitter fairly often about the game's progress, so I'd recommend following her here: https://twitter.com/meyaoigames
I hope all this helps 😊