I had a professor who asked us to print source code for our projects for him to read. Looks like he's still at it. I'm sure he's being driven insane in these AI times.
I can read my code just fine.
Initially, it was much harder to read, both because of the habit I've developed and because, I think, the author also didn't use a "fancy" editor to write their code, so it wasn't formatted properly, didn't observe naming conventions. Well, your typical college professor writing. My first reaction was to type the code into the editor so I can explore it easier. This, of course, also provided syntax highlighting.
Of course, it took extra time. So, eventually, for shorter snippets, I'd just suffer, skipping all the typing part. I later discovered it to be somewhat helpful exercise when using Git diff or other Git commands that displayed code snippets in terminal w/o highlighting. But then the industry caught up to it, and now I don't have to read unadulterated Git output like that.
So, my conclusion so far: highlighting helps to discern the structure, to process larger blocks of code and to navigate it more efficiently. You can get better at reading code that's not highlighted, but it's never going to be as good as reading the highlighted code. It just seems like the struggle to even get to the level where it's palatable not worth it as there are very few situations where it would come in handy.
For some harder C code (implementing `malloc` for example) my preferred debugging method was printing out the code and debugging it with a pen between classes.
I eventually realized being inside an editor gave me too much attraction to thrash with "just one more quick iteration & debug run..." and could actually end up more time consuming than being forced to reconcile my mental model with what I had already written by me double checking my assumptions.
Interestingly, some of my peers started picking up the habit for their own projects and we ended up having small "debugging" sessions by trading print-outs .
Though I also remember sketching programs on paper as a teenager for my TI-83, since it was annoying to type everything out and then have to make a bunch of edits.