The tutorial is kinda hastily put together as it’s just a regular playthrough with a fixed seed that restricts what you can play/discard for the first steps, so adding an option to go back would be difficult (other than within the same set of text boxes).
Your selection in the second screenshot only contains 3 unique colors (blue, red, and yellow), so the upgrade does not apply there. You get less points from it because 9 8 7 gets the sequential bonus (+1 mult), while 9 8 7 5 is no longer sequential.
There are currently only three possible debuffs that boss rounds can have: “Wild cards cannot be played”, “Decrease queue mult by 1”, and “Not allowed to discard”. I suppose “Decrease queue mult by 1” is the most unclear as instead of a restriction in the player’s actions, it just decreases the queue mult by 1 (usually the queue mult starts at 2, but the debuff makes it start at 1 instead).
I assume by audio you mean the music. I was wondering why nobody complained about the music as I’ve always found it insanely repetitive. Maybe if I can up my music skills the next version will have a more listenable track.