The Katrina white shirt PPV with her toys was taken before the Darren bar stuff (in Elise's apartment) - so it's a different white shirt from the one Vanilla teases MC in Darren's apartment... but looking back I can see how that might be slightly confusing as while playing the game from MC's POV you unlock the PPV the day after the Darren event (after Vanilla has sent MC pics of her in Darren's white shirt) but if you keep up-to-date with Vanilla's POV they talk about that PPV before the Darren stuff happens which makes it a bit clearer - I guess I just had a thing for white shirts that update and ended up using similar outfits in 2 separate scenes
As for how to make a game like this... it's just about learning programming and how to make UIs in Godot or another game engine and putting those together to make a game