Hello, I've just come across this post and I have an idea of how to make it work, if you haven't got it already :))
I've just gone into Construct and tinkered about to make something work. It might not be exactly what you're looking for, but you could have it as a placeholder until you've got what you need?
So, you could create a different sprite for each quest, with the text and the checkbox as one, and then have an additional Animation to each one, which is the box being checked.
I didn't actually do that, I made one text box that stretched down the length of the quest box and then typed out the first set of quests, and put individual checkboxes down beside that.
What I've done is given the illusion of scrolling, and it's quite simple.
Make sure that the "Mouse" function is added to the layout, which will open up the option to use the mouse wheel scrolling within the code.
With each checkbox being individual sprites, you can ensure that once the quest is completed, you can make the check appear to show you've completed it.
I'm not sure if this has made any sense, so here a screenshot of the entire code for you to have a look at :))
Here's also what I've put onto the layout, just in case I've taken you down the completely wrong way, then you can tell me lol ....
I hope this has been at least vaguely helpful for you!!