The "keep practicing with Falsetto" quite often has a bug in which a girl sits there and prevents Alex from continuing.
That girl is Falsettos whore and the action you can witness in the second quest. Meaning technically that quest started ...
But since that girl actually does not leave because HER short introduction event did not start and at the same time is blocking michaels introduction event ...
What triggers that bug is unknown, as is the fix to that. Forcing the event by save editing or via console does not work for some reason.
Long story short you sadly are forced to start a new game. Maybe reverting to an earlier save "is enough", though.
I think the first 2-3 times I send Alex to Falsetto's studio there were some sex scenes with a girl and a guy on the balcony. Once together and a couple of times alone if I remember correct.
Also I might have send Alex to Falsetto's studio between she got the task of selling his equipment and actually got it sold. Not sure if that's what breaks the quest.
Beside that. I'm still missing a lot of the characters according to the characters gallery, but I only have 4 quests left. The 2 involving Falsetto, one saying "Develop relationship with other character" and one without any text. I have a hard time making out the portrait next to the missing text, but I think it's Rudo. I've also unlocked the porn shop, old town, and south district, but never seen any quests involving either of them. The psychologist location in the hospital disappeared shortly after I unlocked it, and there has never been a quest involving the gynecologist despite Alex has been pregnant and has an abortion.
In Barbara's gallery, it says Alex can "fuck her with a strap-on in the kitchen", but I never get that option, when Alex see her in the kitchen, and I haven't been able to find a strap-on in any of the shops. Nor the sex shop, porn shop, online shop or anywhere else.
So end of the day. This game seems very buggy, and it seems like I'm missing a lot and no way to unlock new quests. So I think I'll just ditch it instead of starting over, or go back to an earlier save.
Should anyone have console commands to trigger some of the missing quest, please let me know.