Hi there,
Sorry to hear you are having problems, the game shouldn't softlock due to Holly's quest being a side quest, at least it's not a bug that's been reported to us while we developed the game.
As you've already said, using old saves and data from the demo or any other version except this final version, can cause errors as old code was changed that the saves might be lacking.
That being said, I'm not putting it past something to have slipped through, despite the amount of testing the game went through on Patreon. Can you not go to Kitty Burger and ask about the uniform? or has the option to access the map disappeared? The map disappearing usually means there's something you need to do before leaving the area.
Please let me know, if you are still having trouble now you've started with a fresh install.