Further to this there are some BUGS with the Lesson module in that it clashes with Bootstrap 4 CSS in some places, also the form layout used to display the questions is also affected hence that big gap between the questions and the left-hand margin.
This last problem relates to a Moodle Tracker that I was assigned to, and was almist fixed with either earlier this year or last year, I forget as time flys by so fast!
It is related to that extra column you highlighted, the reason it was not fixed is that it conflicted with some templates in Boost theme.
I am now trying to solve another issue in the Lesson module if I can but not too confident about it as Lesson is an old module with some outdated code.
A challenge...worth doing.