Eh? I just did "clean installs" of each week, including deleting the system-wide save folder before launching each one. The DM button was present on the title menu in each case.
Well it wasn't for me, I would go and screenshot it, but I already deleted the game.
From what I remember when booting the game, there were the obvious menu choices obviously, but there was no setting that said "Dark Mind" in both the in game and main screen menus.
I only noticed it because I wanted to see if there was some way to change the decisions I made in the game without having to replay a couple of days, long story short, that didn't work because almost no games allow that, but it got me to thinking to associate the butterflies with buttons, I see that there is a butterfly in the Save/Load menu and that's when it hit me, this is where the Dark Mind stuff was and you could imagine my face.
NOTE : I didn't relocate the Dark Mind stuff from when I downloaded the game to when I "rage quit", it was always in the proper place since it was in the game, just very hidden. Then I started Day 4 and saw one of the daughters slobbing on my knob after doing nothing in the first 3 day, I was so shocked and thought about all the content I missed out on.
But I don't blame the dev or myself really, I blame Patreon for having developers hide this stuff in the first place, it's just a game, I can assure you I never had any incestuous feelings towards my 2 real life sisters or any of the other Dark Mind contents towards anyone.