I'm sorry Timmy but you're not allowed to have any dessert unless you close your tags like I taught you. Your grandmother was XMLish and you need to carry on our family tradition.
I thought you might do something like this so I got you a backup one from AO3.
The actual thing that matters is that the / is ignored so (unlike with XML I believe) you can't self-close a non-void element by adding a trailing /. But "void elements should not have trailing slashes" is extrapolation on your part; the trailing slash improves readability and is kosher since it doesn't act as a self-close.
TIL. Funny thing, though, is that they give an example of how to use <br> and have it with trailing slashes. And then explain that trailing or preceding slash will be ignored, anyway ¯\_(ツ)_/¯
It's actually more confusing/less correct to close bodyless elements in HTML. Since HTML treats "/>" the same way as ">" which could lead to a "/>" tag not actually being closed, if it is used on a non-selfclosing tag.
We had a class in the first semester of uni where we had to create a static html page based on a screenshot.
There was this one textbox at the top of the site, where the only way you could recreate the screenshot was by using a <br/> in the middle of the text.
The prof was very picky about your HTML being semantically thorough and correct, so that was super weird that that was necessary.
You can style your whole webpage with divs, but using main, nav, footer or whatever blocks is semantically more correct, because you group elements together that have a certain purpose.
A HTML Tag in the middle of a sentence is not wrong per se, but when parsing it a line break could signify two sentences where one has missing punctuation, instead of a complete sentence as your original intention was.
I don't really care how the design you want is achieved to be honest, but I don't get why the prof didn't argue against.