Hiya! I apologize if this is in the wrong area--If I have made a mistake, please feel free to call me out on it. Im a silent lurker for the *Most* part, and go through NUs in "sprees". I recently returned and started reading novels again and found that I am Missing the checkbox next to chapters when pulling up a series, and the refresh icon that I think was to allow you to say "I read everything up to here" or something like that. I would post a picture, but I am not allowed to due to my low post count and do not want to try cheating a url into the post without permission. I humbly request assistance.
Go here: https://www.novelupdates.com/reading-list/ Under Global Settings, check the boxes for Enable Reading List and Enable Quick Add.
I used to think his was for checkboxes too, only fairy recently did I find out this is actually just for: As long as "Enable Reading List" is ticked under Global List Settings, checkboxes will appear. The refresh icon is hidden under the "book" icon (show me chapters I haven't read). If you want to have it separate, like in the past, you'll have to disable reading list notes.
Better cover all the areas, since the check boxes doesn't specify the list they're sorted into until after you've first sorted it into a list.