When I mark a word (of any kind) I would like all occurrences (in that particular file) of that word to be highlighted in the scrollbar on the right hand side.
This
This was a feature in VS15 and VS13.
Actually it was not.
It is a feature of the Productivity Power Tools extension. That extension is now just an installer for separate single feature extensions. I think you'll be wanting Match Margin.
Right now, the only way I know (without installing new extensions) is to select (double click) the word and hit ctrl-f (find). Scroll map should highlight all occurences (mine are orange)
There's another extension which does exactly this, with options to customize colors and more. it called Word Highlight With Margin.
The extension created by Trung Kien Phan
Download link from Visual Studio market place - VS2017, VS2019
VS2015
VS2010, VS2012, VS2013