Hi hi! Yes I'm always happy to help people learn about Godot especially if they wanna make VNs in it ^_^
The overview of it is that we used Godot 4.2 (and now I use 4.3 so the latest releases are all good) along with the Dialogic 2 plugin which helps us manage the dialogue. Dialogic is also a helpful plugin for people who are just getting started with Godot since Dialogic can handle your dialogue, your backgrounds, the audio, sound effects, sprites, etc.
We didn't actually use Dialogic for anything more than the dialogue and saving some save file variables, so in Good Lord! The music and all the visuals run on a separate system that I coded from the ground up because Dialogic doesn't have the full range of flexibility we wanted for animations and music cues. Fortunately it's very easy to get all that connected and it was a pretty smooth process!
I also coded another VN demo in Godot if you want to take a look at a very different style of VN too (BDWA Radio). OH! Also I'm giving a talk about this at VN;Conference on the 25th too so that talk will be recorded up on their youtube after the fact too if you can't make it.
I'm glad you all enjoyed the game too and feel free to reach out if you have any questions too!